It's funny, I think most of the best music comes from jolly old England. Eric Clapton, The Beatles, Led Zeppelin, and The Who are all among my favourites, Clapton especially.
I think the most underrated band ever, and my favourite band out of the USA would have to be the Allman Brothers. Despite being a cowboy, that's really the only country music I listen to (and it's more rock/blues anyways). Besides Johnny Cash, but everyone listens to him. All you rock/country fans definitely holler at me if you like the Allmans.
I also love Bob Dylan for his songwriting and grungy voice, as well as Jimi Hendrix for his out of the world guitar skills.
Rock is probably the best genre, but like a lot of my sheep-minded peers in middle school.. I developed a taste for hip-hop. The stuff nowadays is just garbage, but I love the rap in the 80's and 90's like The Roots, A Tribe Called Quest, Nas, Rakim, and the Wu-Tang Clan. Basically the kind of hip-hop that actually has intelligent lyrics.