The aging SlingPlayer for Windows Mobile has been updated, and almost exclusively for compatibility. The app will now run on most modern phones, including (finally) 640x480, 800x480, 400x240 and 320x320 handsets.
The official list of supported phones now includes the following:
Sprint Treo 800w
Sony Ericsson X1
Palm Treo Pro
Sprint HTC Touch Diamond
Sprint HTC Touch Pro
Verizon HTC Touch Pro
Verizon Samsung Saga
Verizon Samsung Omnia
AT&T LG Incite
AT&T HTC Fuze
AT&T Samsung Epix
HP iPAQ 910
AT&T Pantech Duo
Sprint Samsung ACE
Verizon XV6900
That said, almost any phone running a compatible resolution should be fine (Touch HD, anyone?). [Sling]