reddit, mostly. I swear every time I read a discussion there the prices are silly.
Coming from a person who frequents reddit and enjoys it quite a bit over there at times, btw. It has its place, but the explosion of people has had some interesting side effects. Especially when coupled with the rest of the reddit ecosystem's culture.
EDIT: You should see the market for Korean customs. I thought I paid a pretty large sum for mine and I'm fairly confident even I could make a sizeable profit currently.