I've been looking into Verizon ones for Page Plus. Frontrunner for me has been the Samsung SCH-i760. WiFi, slide-out QWERTY keyboard, Windows Mobile 6.1, full Page Plus compatibility with no hacking, and available for under $100. The HTC Ozone is supposedly better, but it's $200+ without a contract since it's so new.
Since you're also interested in GSM, which carrier are you looking at? One with a prepaid plan? I haven't done much research into GSM phones since I am on Verizon and I'm interested in Page Plus for the robust network. Any other features you want - touchscreen vs. physical keyboard, OS preference?