Aradhana, how fun! Here is my suggestion for an itinerary, however I can tell you that moving between so many countries will not be cheap -- especially Switzerland! -- Your choices of transport are either train or plane -- one costs more money but less time, and one costs more time but less money. It's always a tradeoff!

I'm not sure where you are starting from, but I would say that London is a good place to fly to, since you can then fly just about anywhere easily. You then go to Munich second, because Oktoberfest only goes until October 4 -- and work your way back to London to fly home.

Day 1 (Sept 27) - Arrive in London, rest
Day 2 (Sept 28)  - London
Day 3 (Sept 29) - London
Day 4 (Sept 30) - Leave London in AM, fly to Munich
Day 5 (Oct 1) - Munich/Oktoberfest
Day 6 (Oct 2) - Munich/Oktoberfest
Day 7 (Oct 3) - Munich/Oktoberfest
Day 8 (Oct 4) - Leave Munich, fly to Switzerland*
Day 9 (Oct 5) - Switzerland
Day 10 (Oct 6) - Switzerland
Day 11 (Oct 7) - Leave Switzerland, fly to Amsterdam
Day 12 (Oct 8) - Amsterdam
Day 13 (Oct 9) - Amsterdam
Day 14 (Oct 10) - Leave Amsterdam, train to Brussels
Day 15 (Oct 11) - Brussels
Day 16 (Oct 12) - Brussels/Bruges
Day 17 (Oct 13) - Leave Brussels, train to Paris
Day 18 (Oct 14) - Paris
Day 19 (Oct 15) - Paris
Day 20 (Oct 16) - Leave Paris, take Eurostar to London
Day 21 (Oct 17) - depart London for home

Must see in/notes for London:

• Tower Bridge and the Tower Of London - touristy and cheesy but necessary if you've never seen them.
  
• London Eye and Southbank Centre/Southbank near House Of Parliament.
  
• Camden Town and the canals - great shopping and culture.
  

Must see in/notes for Munich:

• If you haven't booked a place to stay -- BOOK NOW. Everything in Munich sells out.
  
• Visit the English Garden and Glockenspiel for a bit of Munich sightseeing.
  
• If you have time, take a day tour to Neuschwanstein Castle - Cinderella's castle in the south of Germany!
  

Must see in/notes for Switzerland:

• *I'm not sure where you want to go in Switzerland, so I can't really provide suggestions. Just know IT IS A REALLY EXPENSIVE COUNTRY.
  Doesn't matter what city, it's going to cost A LOT to visit/stay/eat/sightsee.
  

Must see in/notes for Amsterdam:

• If you're brave, visit the Red Light District and see some "culture" there.
  
• From what I've heard, Amsterdam is well-accessible by bike or boat, so look for biking or boating tours of the canals!
  

Must see in/notes for Brussels:

• Visit Grand Place and Manneken Pis. I also had a great dinner at Nuetnigenough nearby.
  
• If you can, take the train to Bruges and walk around for a few hours. It's a beautiful town, and there are great foods and beers there too!
  
• Be sure to have: waffles, beer, fries, and chocolate. Belgium's four best foods!
  

Must see in/notes for Paris:

• Eiffel Tower and Notre-Dame de Paris are both touristy, but well worth it -- show up early in the day to avoid lines!
  
• Climb the hill at Basilique du Sacre-Coeur to look out over the city.
  
• The best ice cream (some say in the world) is found at Berthillon on the Île de la Cité. Also, be sure to try macaroons from Pierre Hermé Paris.
  
• I loved the Catacombes de Paris tour -- it's my favorite unconventional thing to see in the city.
  

Have an AMAZING trip! I wish I could go along on this trip, if you follow my itinerary :)

You should allow at least 3 to 4 days in each cities.  It will give you a good idea of the place for a first visit.  Also plan one day for travelling between cities.  So you eather have too many cities or too few days to go arround. 

Hi!

You can see Paris in 4 days, London in also 4 days, Amsterdam in 3.

I think the best way to discover Amsterdam is by bike, you can rent one and you can easily visit everything. When you are in Amsterdam you are not far away from Volendam or Zaandam, typical dutch cities.

Have a great trip!

As previously mentioned, Brussels ain't that funny. I would not skip it altogether though since it is an interesting city. But maybe just spend one day there. My personal "must see"s in Brussels are:

• Atomium (the coolest building I've EVER been to).
• Belgian chocolates! Lots of exclusive shops selling that.
• Parlamentarium (The European Parliament's Visitors' Centre - if you find that interesting. It's at the Willy Brandt Building, Rue Wiertz 60) 
  

In case you choose to not go to Brussels, you might just consider to transit at their airport. It's HUGE and you can buy lots of chocolate and other treats in the shops there. 

Amsterdam is a quite small city and unlike London or Paris it does not take that long a time to go between places. I would stay 2-3 days in Amsterdam. Must see's are:

• Just walking around, looking at the bridges, the water and the narrow houses.
• Eat pancakes at De Carrousel Pannenkoeken (at Tweede Weteringplantsoen 1)
• Vondelpark (beautiful park)
  
• A museum or two. But keep in minds that cues are generally long (with a LONG waiting time) and the venues are crowded. When I visited the Anne Frank House it was so crowded that I couldn't really experience it at all.
• Jeanneke-Pis - the less famous statue of Brussels. The peeing boy gets all the attention but the girl is locked away behind bars in a small alley. Quite hard to find but she's located in a wall by the outdoor seating of Delirium café.
  
• Since you're going to October fest I guess that you're in to beer. You might enjoy a visit to Heineken Experience

I would avoid the Red Light District (it's quite depressing with families and children looking at sex workers like animals at a zoo).

When it comes to London, I would stay the longest here, at least if you haven't been here before. There is just so much to do!

• Pick one or two of the many museums of London. The British Museum is amazing but depending on your interests you might enjoy Tate Modern, Natural History Museum, Tower Of London or The Sherlock Holmes Museum more.
  
• Go see a Broadway show! Or, of musicals aren't your thing, visit Electric Cinema - a luxurious yet cozy cinema experience. 
• Read up on London before you go and decide if there are any parts that are of particular interest to you. You might wanna go to Camden Town and Camden Market (once the epicentre of punk, goth and also hippies, now a center for shopping - but still really fun to see) or visit Big Ben and other landmarks. Or you might wanna walk in the footsteps of some musical icon?

Regarding Paris, Octoberfest and Switzerland I'm not the best to share advice so I'll leave that to others more qualified. :) Have a great time in Europe!

If I can make one suggestion?  Skip Brussels.  The city has it's charms of course (and lots of yummy chocolate!), but in my opinion it's not even in the same league as the other places you mentioned. AND it's expensive. 

On that note - all these places are expensive, but certainly there are ways to go cheaper. Depending on your travel style, hostels can be a good choice. Switzerland in particular has some lovely hostels. Beware of the very cheapest options in London and Paris, but the more expensive ones can actually be VERY nice for the price. You might also consider AirBnB as an alternative or Couchsurfing!

A few notes:

Paris - you can get a cheaper meal by going to the market or a grocery store (or La Grande Épicerie de Paris) to pick up cheese, bread, fruit, etc. I personally love the sandwiches at Cosi, and they're not too expensive either.  My absolute "must-do" recommendation is Versailles. It's only 30 min by train from Paris and is absolutely fantastic. To save a bit of money (and time), skip the tour of the palace and just go into the gardens. Have a picnic. Rent a bike. You'll love it. Guaranteed.

London - you'll never see it all in a few days, so don't knock yourselves out trying to. Just try to hit one museum (my vote is for either The British Museum or Tate Modern), one government/royal thing (Buckingham Palace or House of Parliament), one historical site (Churchill War Rooms or Westminster Abbey) and one outdoor spectacle (Big Ben or Trafalgar Square). Then just pick a neighborhood to walk around and get to know! Once you've done all that and had a bite and a pint at a pub, you'll have sampled London for sure. Alternately - a bus tour really does help you see a lot in a little time!

Switzerland - Geneva can be easily done in a day. But you really want to get out to the countryside and mountains. If you can get to Interlaken it's a perfect jumping off point for hiking or more extreme mountain sports. Thun is a favorite city as well. If you're looking to stick close to Geneva, there is plenty to see and do near Montreuxand Lausanne - like Château de Chillon.

Have a great time!

London is worth at least 4 - 5 days minimum.  Paris minimum 3-4 days if you've never been before. Amsterdam, 2 - 3 days is fine.  Switzerland2 - 3 days. I'll leave the rest up to the Trippy universe to answer.  

I would fly into Munich and enjoy Oktoberfest for 3 nights.  Then take an Intercity Bus (around 20-50 euros- 4 hours) from Munich to Zurich.  You don't say what you want to do in Switzerland, but you can get to most places in Switzerland from there.  Stay 3 nights in Switzerland, and then fly from Zurich to Amsterdam (100 to 175 euros)  Stay 3 nights in Amsterdam, then take a train to Brussels for 2 nights (45 to 90 euros- 2 to 3 hours).  Take a train from Brussels to Paris (43 to 90 euros 1.5 hours) and stay 4 nights there.  Take the Eurostar from Paris to London (53 euros- 2 hours 20 min.) and stay there for 4 nights, before flying home from there.