The best by far is RCGroups in the classifieds section. 99% of the sellers on there know the gear they're selling intimately.
However, beware of scammers. There have been a couple lately. You know they're scammers because they insist on you marking the paypal transaction as a gift, which removes the seller's fee but also the buyer's protection...
Otherwise, pretty much all my FPV gear is from Hobbyking. Their range of stuff is respectable and prices are lowest. They've just added the ImmersionRC EZUHF system too, and will be selling antennas shortly.