When Turd started referring to Lind-Waldock, I opened an account there. It certainly is Cadillac.
But for a very basic service, which is perhaps the least expensive site I have seen, and very user-friendly, I don't think you can beat TradeKing.com
Haven't seen it mentioned that much, so figured I would give it a shout out. No holds. Easy to start up. Wire money same day. Not much to complain about!