The E61 is pretty good for the price. I'd get that if I were primarily using it for Push Email w/ WiFi.
If I were going the smartphone route The Nokia N95 is a sweet phone, also with WiFi.
Finally, if you are going full PDA you can't really go wrong with HTC Wizard / 8125 / 8100 / MDA (USA) / K-JAM. Both T-Mobile and Cingular have thier own version of the model so you may be able to get a deal through them. It has Windows Mobile 5, a large screen, full slide-out QWERTY, stylus and of course WiFi.
If you want to look at other WiFi offrings click on the sorted list below:
http://www.phonescoop.com/phones/finder_results.php?m=s&w=s&rar=0&wer=0&plr=0&ttr=0&str=0&dsr=0&atr=0&g8r=r&f60r=r&s=we
