Tough topic to answer, as there are so many influential bands out there. I'd have to say the Top 10 Rock bands (I guess we're putting Metal in here too?) would be:
1. The Beatles - like Jason said, without The Beatles, there would be NO rock music, period. They invented rock music.
2. Guns N Roses - Solely responsible for the resurgence of Rock music in the mainstream, if you ask me. Took what The Stones did and kicked that
up a notch. Back in their heyday, GNR were bigger than The Beatles were in their
heyday - and that's something. Never been a bigger rock band - almost overnight at that - and there never will be.
3. The Rolling Stones - took what the Beatles did and kicked it up a notch or two. Louder, harder, and (slightly) faster at times, it was a true progression in the sound of music at the time.
4. Metallica - re-invented the Metal genre, taking it away from the hair bands like Ratt and Poison, and making arena rock safe (well, maybe not safe) for all.
5. Black Sabbath - the inventors of the Heavy Metal genre. Without Black Sabbath, who knows what rock/metal would sound like today - if there even would be such a thing?
6. Nirvana - As big a PJ fan as I am, I would still have to say that Nirvana were bigger - and more responsible - for bringing the grunge/Seattle sound into the mainstream. They were the first Seattle band to have any commercial success while still doing what they wanted to do. They never intended to be rock stars, it just happened.
7. Slayer - taking what Metallica did and re-inventing it into a faster, harder, more aggresive sound, they are the grandfathers of the Death/Thrash/Speed Metal sub-genre of Metal.
8. Nine Inch Nails - Trent Reznor is a musical genius, if you ask me. Again, taking parts from different styles of music at the time and re-inventing a "new" style, slightly techno, slightly industrial, slightly dance/club oriented, yet still on the harder/metal edge, he's just a innovator and a big influence to many musicians out there today.
9. Led Zeppelin - okay I have a confession to make. Being a musician, and a huge fan of music in general, this is gonna get me a lot of flak, but here goes: I think Led Zep is overrated. One of the most overrated bands in music history. That said, they were still a huge influence on music, and the sound of rock at the time. They opened the doors for bands like The Doors, Deep Purple, Iron Butterfly and all the other psychadelic 70's rock bands. But that doesn't change the fact that I don't like them. And the fact that I don't like them doesn't change the fact that they were a huge influence on music.
10. Elvis Presley - okay, maybe not a band, per se, but as much an influence on modern rock as The Beatles. The most dangerous man on television