Super Mario Bros. 3- It's a timeless classic- I still probably haven't found every bonus room in the game. Even after beating it, I'll still want to come back to play it as the level design never gets old.
Battletoads- I've never played this on an actual console, but I hear it's very difficult- something I'd always like to play. Considering I'll have thousands of hours to kill, this doesn't seem like a bad choice even on impulse.
Ninja Gaiden- Also a very tough one- it'll be fun to tackle after BattleToads.