Voicestream is another good one. The Nokia they supply is generally better than AT & T's (6190 vs 6120,60,61) unit. Also, Voicestream is GSM, so you get a lot of nifty WAPesque features...you can also get new ringtones and logos sent to your phone straight from voicestream's website...no need for cumbersome data cables to your PC.
You'll also see Voicestream under the Omnipoint name, though they're phasing that out.