Before you upgrade, ask yourself what you want to do with your PDA. If you like reading e-books, make sure you got one with a decent resolution (those 640x480 VGA Pocket PCs are gorgeous!). On the other hand, if your main goal is to organize your days and phone numbers, you may as well consider buying a Palm handheld (e.g. a Palm Treo).
Anyways, welcome to Mobileread!