You should stay away from expensive models for your first pick. Making a list of what you want to do is a good idea.
If you need connectivity, then having built-in WiFi or BlueTooth (or both) is important, as it will save you the expense and burden of add-on cards.
Checking the number and type of expansion slots that you want is important too. If you only intend to have a small number of apps and stay out of gaming/video, then anything will do. If you want to watch videos, then a CF slot could be an important factor, as CF memory is cheaper than SD.
Form factor could play a role too, for you. Some people don't mind large PPCs (Ipaq 5550, Toshiba E800...) while others prefer much smaller ones.
Some good initial picks could be the Axim X3 (WiFi, one SD slot), the Axim X5 (very cheap from Ebay, dual slot), an Asus A620BT, a Toshiba E400, an Ipaq 1910 or 2210...
