Most influential (no order):
NIN
Nirvana
Limp Bizket
Oasis
Rage Against the Machine
Best:
Garth Brooks (this is hard to say from a country-music hater)
Nirvana
NIN
Verve Pipe (ok, that's a personal favorite)
Matchbox 20 (possibly mest non-alternative rock band of the 90s)
Greenday
Oasis (European following)
and I'm going to say this one seriously: Bloodhound Gang (They are actually a very large band in Europe from what I understand. Figure that one. But if I'm wrong, then they shouldn't be here)
Alice in Chains
Pearl Jam
probably many more
As a side note, this is the first 100+ post thread I've read the whole way through in a long time. Another note, whoever necro'ed this should be put to death...19 months old!? Probably 10% of the people posting in this thread have been banned!