From an RPG Bloggers meme that's going around-- spotted on Risus Monkey and Huge Ruined Pile most recently.
2. Call of Cthulhu
6. Superhero 2044
7. Final Fantasy Tactics
8. Exalted Dragon-Blooded
9. Dungeons & Dragons (Blue Box)
10. Monsters, Monsters!
11. The Enemy Within Campaign (WHFRP 1e)
14. Valkyrie Profile
15. World War 1
For the next five, I'd add Gumshoe, James Bond, Ars Magica, SMT: Nocturne, and Lace & Steel.
That's without thinking about it too much off the top of my head. Crap the more I think about it the more I come up with stuff...what about the original Heritage or FASA Star Trek role play...?