I saw a link for a Palm-based GameBoy emulator, then was stunned to read about an Atari ST emulator for Palm. A quick Google search later, and I found an Apple //e emulator too!. It’s the old-timer in me, but I really enjoyed the games on those old systems.
More info on the Apple //e emulator for Palm are at Palm Info Center and FreewarePalm. PalmEmu links up a number of emulators for Palm.
[UPDATE]: There’s a review of Palm-based emulators at The Gadgeteer. Thanks to MyPalmLife for the pointer (look there for more info too!).