Thailand forum

I'd say that great street food is everywhere, but also that some places are better than others.

See Travelcook's question (a couple of posts below yours) for info on some of the areas, particularly Sao Chingcha (Thanon Tanao and Thanon Dinso).

Personally, despite their popularity, I think that the food stalls on and around KSR, for the most part, are awful. I don't include Thanon Phra Athit or Phra Sumen, or the little spot at the top of Soi Rambuttri with these places, though, as each area has its gems.

You can find bad food at expensive restaurants. Most Thai street food I've tried was just ok. Some of it was pretty good.

The best place to start looking would probably be the wet markets.

Riedez

I hope this helps
http://migrationology.com/index.php/2011/05/top-16-bangkok-street-food-sanctuaries/

Riedez

I hope you take a look at the other post by travelcook and that is mentioned by Tilapia. The link is here.
http://www.travelfish.org/board/post/thailand/14689_native-dishes-of-bangkok-and-thailand

There are a few more links and suggestions there. The migrationlogy website also has a few suggestions.

I found this thread at chowhound.
http://chowhound.chow.com/topics/566631

On facebook, there is a page for Cheap Eats Bangkok. You can look at their photos and their map.
Here is a link to their map
http://bit.ly/mHUEtO

As Tipalia says, street food is everywhere, but in my opinion it is best outside of Bangkok, in the night markets that come to life in almost every little provincial town (just like MADMAC says). In Bangkok, however, I look for the indoor food courts that are typically on the upper floors of most shopping centers. The food is only slightly more expensive, but in my experience higher quality and certainly generally cleaner/safer (if only because of less dust and vehicle exhaust). Good variety and a fun, local atmosphere at those indoor food courts too. Give them a look. Cheers.

There's a place on Soi Rambuttri on the left hand side past the first 7-11. Its basically a VW camper van that parks on the side of the street. The lads there open up the back of it and have a big flat screen TV there where they show the footy and other sports. They set up loads of little tables and chairs and they sell beer and cocktails at cheap prices (70 baht for a large Chang or Leo). A few metres up the road from them is a Pad Thai vender who makes the tastiest Pad Thai I've ever had, and spring rolls and bbq chicken. You can bring your food down the the tables I mentioned above and hang out there for the night. Its a great spot to meet people. Myself and my girlfriend regularly hung out here and had some great nights. They set up about 8pm and stay open till about 2 or 3 am. Check it out.