I've used successfully Lucent Tech's and Orinoco's Silver cards. Seem to be very reliable and fast. Silver cards have 64-bit WEP encryption, but Gold cards would have 128-bit, so it might be slightly better and I don't see why those wouldn't work on Amiga either. It's an another question does that improve security in practise though.
Prism2.device works with those and you can check it's documentation about other supported cards. There's big list of cards which should work in theory. Shouldn't cost too much to test either as you can find those kind of cards very cheaply on used stuff markets.
