Genre: Urban Fantasy/Modern Horror
System: HERO, using Dark Champions, Hudson City, and Urban Fantasy HERO as primary books.
Concept: Secret group investigating and combating the paranormal. Think of Torchwood meets X-Files, perhaps with doses of Supernatural (which I've never seen, but have read up on the concept), The Dresden Files, the Anita Blake series (before they became nothing more than preternatural porn), Call of Cthulhu, and the like.
PbP or face to face.
Genre: Typical fantasy RPG, using the Greyhawk setting
System: HARP (from Iron Crown Enterprises)
Concept: Greyhawk setting using HARP instead of D&D. However, this may change depending on whether or not I want to complete my deity list or just convert the Greyhawk deities.
This one can be done online or face to face.
Genre: SF/Psychological horror
System: TimeLords from BTRC. Or GURPS 4e. Both modified heavily with house rules.
Concept: Everyday normals thrown into a not-normal situation, with highly unusual discoveries about themselves.
Since not many people know TimeLords, the GM would control most of the character sheets. For GURPS, the GM controls some aspects of the character sheets, keeping a few things secret.
Good one for PbP, though it can also be done face to face just as easily.