The Beatles, Led Zeppelin, and Pink Floyd are the three bands whose music and influence separate themselves from the rest of the pack considerably. However you want to order those three is up to you.
Currently, the best three bands is a revolving door, although I think an extremely over-looked group is Minus the Bear. I urge you to listen to them; if you can find their new, leaked album online (it's pretty easy to do) I suggest getting a hold of it. And that's coming from someone whose father is in the music industry, and someone who strongly is against downloading music; that's how profound I think their talent and musical/lyrical genius is.
non rap is the White Stripes and really nothing else is close rap is Kanye West, Eminem, and Mos Def. There aren't many CD's I would pay for or look forward to coming out, or would get before listening to, but the 4 acts listed above are it.
I also have 5-6 Alice In Chains songs on my iPod from the greatest hits album. They're a solid band too. Look up Rooster on wiki.