I recommend a BlackBerry. The Pearl is really nice if you want the regular phone size, and the 8700 is awesome (but its gonna be replaced by the 8800, which may have wifi) if you want the larger screen and full keyboard.
The Motorola Q, Samsung BlackJack, T-Mobile Dash, Cingular 8525, and the various other "BlackBerry Clones" tend not to be bad, and every carrier has one.
The Treo is good, but it tends to be on the pricier end, and isn't nearly as shiney as the BlackBerries.
I have a BlackBerry Pearl, and I really love it. The screen is amazing, the scroll ball far outshines the various click wheels, and it can play MP3s and video. If you grab it with a plan you can get it on the totally cheap, as well.