SPORE for the PC

Spore starts you out as a single-celled organism and lets you evolve into a water-based creature, then a land-based creature (shown in this gameplay demonstration movie), and eventually a space-faring civilization.

The creature editor looks cool, but I worry that the game is too many games put into one. That usually means everything in the game is lackluster, like The Movies, which was neither a good movie-maker (terribly locked in, creatively speaking), nor a great management/sim game.