Best restaurants for an after work bite to eat/happy hour?

I agree that Euclid Hall Bar & Kitchen is always a good choice. I also would say that Stoic & Genuine is a fun seafood option, it is run by the same chef group as Euclid. If you walk over the freeway to the highlands you could hit Linger or Root Down. A short cab ride to the south side of Cap Hill would get you to Charlie Brown's Bar & Grill, it's a culinarily dicey piano bar that used to be a haunt for Kerouac and the Beat crowd in town. If you are into noodles and broth you could check out Bones... It's a noodle joint opened by another pretty prolific local chef (Frank Bonnano) that is worth a shot. Overall Denver has a lot of pretty diverse options, ask around for what's hot that week.

What PART of Denver? Assuming downtown since you didn't specify, try Mario's Double Daughter's Salotto for a drink or Wynkoop Brewing Company for beer and hokey local flavor. Sing Sing ain't bad for a night out and Linger for your hangover cure breakfast in the morning.

Sushi Sasa is great! 

ChoLon Modern Asian Bistro and Uncle are all fantastic if you like Asian food!

Hi Drew, Denver is great with roof top patios and outdoor space now that its getting warmer. Los Chingones is a great roof / happy hour in a neighborhood call RiNo. Once you are over there, there is a lot of other good bars / restaurants within walking distance that stay busy until 2am. Another great option is Ale House at Amato's in LoHi (we like our 4 letter abbreviations), looks for the bartender Kevin, he's the man. Again, good options within walking distance. Lastly south Broadway has a good nightlife scene, not quite as good for happy hour but still solid. Try Cho77 or LEÑA.

I second Euclid Hall Bar & Kitchen - great sausages, beer, etc. 

If you want to get slightly farther from LoDo (highly recommend exploring neighborhoods, which is where the real cool stuff lives), go to Gozo for what might be the best happy hour deal in Denver (most of their menu is half-off, plus good cocktails and wine list).

Also, RiNo District is perhaps the most bustling part of Denver right now: Meadowlark Kitchen is one of my current favorites for food and drinks. Next door, Meadowlark has a great back patio, and the basement bar gets hopping on Friday nights for a weekly hip hop party called The Solution. Other not-to-miss eateries in the neighborhood are Work & Class (Chef Dana Rodriguez got a Beard Award nomination this year) and The Populist (bring a friend and split the oh-so-affordable seven course tasting menu for two -- only $75 for two and so delicious).