Well if you like high end then there is Blowout Forums. Don't get me wrong you can find lower end sometimes but either way I like so you should check that one out. Also Cardboard Connection & Sports Card Forums are decnt forums where you can trade, buy or sell. If you're looking to sell cards then you can check out Sportlots. Hope that jibberish helps lol.
If you are on Facebook there are several pages. I've deactivated my Facebook account but when I was on there there were some fantastic pages. Very fast responses, actually a little to fast for those of us with families, jobs and other lives.