These are the ones that I'm aware of in the USA:

Group X: Subcompact (2 door)
Group A: Subcompact (4 door)
Group Z: Compact (2 door)
Group B: Compact (4 door)
Group C: Intermediate
Group D: Full-size (2 door)
Group E: Full-size (4 door)
Group G: Premium
Group H: Luxury
Group K: Convertible
Group L: Large SUV (i.e. Chevrolet Suburban)
Group P: Compact SUV (i.e. Chevrolet Tracker)
Group W: SUV (i.e. Chevrolet Blazer)
Group V: Minivan