Nong's Khao Man Gai is fantastic.  Chicken and rice.  Simiple, succulent and amazing. Great lunch option.  While not a food truck, after you sample food cart fare, you would be missing out if you don't finish with dessert at Ruby Jewel Scoops which is right around the corner (428 SW 12th Ave, Portland, OR 97205) and some seriously life-changing ice cream.  If you hit the food cart "pod" on Mississippi and N Skidmore (which is a cool area), then you can hit the original  Ruby Jewel Scoops.  I dream about Ruby Jewel. The ice cream is that good.  And, if you need a coffee or a caffeine fix, try their "Buzz" sundae instead. I want to book a flight to Portland right now.  

My two favorite food truck pods are at SE 12th Street and SE Hawthorne, and at N Mississippi and N Skidmore.  My favorite thing at the former is the poutine at Potato Champion and I love the latter because it's connected to a bar/pub called Prost! and they don't mind if you bring food truck food into their bar.  Gotta love more seating options and you get to enjoy their food with a beer or cocktail!

Two food stands that I really want to try are La Jarochita, which serves Veracruz-style tamales, and Nong's Khao Man Gai for, well, Thai khao man gai.  So please have those for me if you make it there! ;)

Check out Cartlandia on 82nd if you are looking for a Thai food. A place called Anything Else? has the best  go to Drunken Noodles (Pad Kea Mao).

I like Koi Fusion for their burritos or tacos- mexican/korean food. Located all over downtown portland.

My fiancee loves everything from Built To Grill. If you like italian food, this it a must try IMO. (Southwest Portland, Downtown)

Cheers!