I don't find current FreeCiv SDL port playable. Interface is terrible.
I started an effort to port FreeCiv GTK+ interface with proper changes to be usable on small touch screen, but did got practically none feedback.

On the contrary, Dune 2 port is just fine. People reported finishing game with it.
Ur-Quan Masters is also complete and very playable. It's hard to win a battle using N900 keyboard. Some external controller is desirable.

For platformers, you should get a game-gripper. But be warned, this could wear your keyboard faster than normal usage.

Roguelikes are available. My POWDER port is very playable. It has great touch screen controls implemented.