Thanks to maba for the SDL suggestion. Since it's cross-platform, I can do most of my development in my native Mac OS X environment, and then just fire up the Maemo VMWare appliance if I want to actually cross-compile something to try on the device.

All I've done so far is an incredibly basic full-screen "paint white blobs with the stylus" program, but it's really cool to see it run on both my Mac and the tablet.