Mount & Blade : a very good addition, made by two people...you'd never believe it...

http://www.taleworlds.com/

Mounted combat
missiles, arrows that work very well.
skill based combat.

Lead an army, literally...
watch them fight alongside you.

Trade goods, make allies and become rich,
the developers are constantly working on it, once you have the game it can be updated within the game menu.

Simply check it out...

Mount and Blade has a lot of good gameplay, but I haven't had a chance to play it for very long, yet... Mounted combat is really fun.

This was one of my very early suggestions to Greg, but unfortunately Taleworlds wasn't interested in working with us ...

I really dig the game, it's on my "permanent install list" alongside Nethack, Deus Ex and System Shock II.

Actually, they've never actually said "no," but haven't agreed, either... We're still pinging them from time to time.