Yank Sing is our favorite. Delightfully Hot! We find it at asian grocery stores here but you can also order them.
http://www.yanksing.com/to-order/sauces.html

Just adding to apartment cookers advice that companies name Huy Fong Foods, Inc. Good stuff. Yes, look for the green cap.

I agree with Antonia, but I will say one of my favorite brands of chile paste is Sambal Oelek, and it's commonly available in most grocery stores. Look in the Asian aisle - it's has a green cap and is by the same company that makes the Sriracha with the green top!

Here's our technique for sourcing something like that. (My son actually did this when I sent him off, while we were traveling and near a city we'd never been to, to get some red curry paste so that I could test a recipe for an Editors' Pick review . . . . ) Go to an Asian grocery store which carries a number of different brands, most if not all from Thailand. Then, ask the owner of the store, or the manager, and anyone else who's around, which brand they like the best. And the follow up question is whether they actually use it. The red curry paste my son brought back, on the recommendation of the gentleman in the store, was excellent! Of course, this method works only if you have a good Asian grocery nearby. I use this method when purchasing all kinds of things (mostly condiments) in Chinatown. I had my son pick up two cans of the paste, and we still have one. I'll post the name of it tonight. ;o)

Oooops ... CHILE paste (not chili paste).