CellCraft
Topics Covered: Cell structure and function, roles of organelles (mitochondria, nucleus, ribosomes etc.), enzymes. Also, has very cool pictures of real organelles and connects the game to actual structures.
Check out the worksheet that goes along with the game, courtesy of Ms. Julie Olson!
Special thanks to the makers of CellCraft for providing this version for biomanbio.com. If you have had trouble progressing through CellCraft on other sites, this version should fix that problem. I could not get past level one due to network problems at my school, but this version bypasses the problem.