Android
If you don't have AT&T or don't want to deal with Blackberries, your only other solution is to make use of one of the Android phones. Google has been busy updating its Android OS. If you can get a phone that is running at least version 2.0 or better, you’ll be happier with the phone's responsiveness and features.
If you purchase the Verizon-based Droid Incredible, it has ActiveSync built in. Otherwise, the other Android phones are for the most part missing any Exchange client. You'll have to purchase some additional software to make it work properly.