Hi all-
As a few have already mentioned some of the stores in and around the U.S.A.(TRU, K-Mart, The LEGO Store, et el). I will share with you some places that you can buy LEGOS where most would never think about. Ok please be patient and understand that under no circumstances that you are guarunteed to find new or even complete sets at these locations, or for that matter any LEGOs at all.
Living in a city like Chicago, I have learned that you can find a lot of stuff if you just "dig around". The first thing I will mention is second hand stores. They sometimes have things you would have never found at any other store. Mind you you may have to dig through boxes or ask around, but sometimes you can get lucky. The next place is a Flea Market and to tell you the truth I have gotten the best deals on misc. parts and the like at these places than at others. As an example, back in December of 2006, my buddy and I went to one and we were looking around and have not found anything for like an hour, then as we were about to leave, I told him I will check just two more places here and then we can go.
It was a good thing I did for you see not only did I find LEGOs, but a 64 quart Rubbermaid tub 3/4 full of LEGO. When I asked the guy what he wanted for them he told me that they were for his neighbor's kids, but for me he says, how about $20.00 U.S. dollars. No arguement there with that kind of price. But again this all comes down to the willingness to look and may even take up a whole day. Sometimes you get lucky and other times you are SOL.
The final few places that I will mention are Garage Sales, Moving Sales, and Estate Sales. I go to these things on a weekly basis and let me tell you, these are great in just maybe attaining a few pieces here and there, altough in some cases LEGO buckets and sets, like the one I went to 2 weeks ago.
Well I hope that helps and happy hunting.