1. Omnifray (which I wrote, so I'm biased)
2. Labyrinthe (high fantasy, high-powered LARP system run near London, England)
3. something futuristic, maybe Dark Heresy (WH40K RPG, which I haven't played yet) [edit] or maybe CoC which I also haven't played [/edit]
4. something oriental, maybe L5R (on reputation alone - haven't played it)
5. AD&D 1st edition for nostalgia, or maybe Vampire: The Masquerade / oWoD