I second the warning on installing Battle for Wesnoth...!

There's a couple that I like that aren't on your list:

Warzone 2100: A very good RTS game, although you'll need hardware graphics acceleration for it to work properly. The cut scenes make it look a little dated, but the gameplay and in-game graphics are very good.

Widelands: Another RTS, but with a much greater focus on resource management. Also has much less dependence on graphics performance.

Then there's FreeCol: Turn based strategy, good gameplay, but has some performance problems which make it quite annoying at times.

Bernie