HTC Hero on Sprint, with the unlimited mobile-to-mobile calls, text, and data ($70/mo).
I was previously on Verizon with a non-data phone & plan. Verizon's mandatory data add-on to voice was $30 alone (mandatory for any phone with data capability), I thought this was a rip off.
Pros:
Droid app tech is handy.
Almost anything you can do with google web can be integrated into the phone's UI.
If you use Google web services (contacts, gmail, calendar, docs, maps, sky, talk, analytics, etc), it automatically syncs those in real time.
Facebook import.
HTC Sense User Interface is alot like Iphone, very slick.
Plays Flash and Youtube, and web browsing is good.
SD card.
Cons
Being 1rst generation there are some bugs.
No physical keyboard but onscreen one is doable.
Processor can be laggy.
The Samsung Moment (also Sprint) is basically the same droid functionality, but with a slide out physical keyboard. Nexus One is 2nd gen.
I sound like a Sprint salesman.