We have some scammers on the forums here, so if you do not know if you can trust a person?
Just check in the list here.

If you got scammed? Please post here: http://bitcointalk.org/index.php?topic=483.0
Please also post the traders you trust.
If you've traded with someone before and everything went okay?
Post his/her (nick) name here. (ofcourse, websites that accept Bitcoin payments are good too!)

Anyhow, I'll start:

• BitcoinMarket
• Theymos

_{edit: I trust Theymos and BitcoinMarket!}