President Forever: 2004
This is neat — President Forever: 2004, despite its weird title, is a surprisingly deep and absorbing simulation of presidential election politics. The demo lets you play a few rounds as Bush or any of the Democratic challengers, and the full version adds a candidate editor, additional campaign years (1960, 1980, and 1992 are promised to registered users), and it only costs $12 to boot!
There hasn’t been a good political game since the venerable Power Politics (which came out in 1992 — jeez, twelve years ago!), so this is a real find.