This is quite a tough question. I am not going to get into who I think is the best band, however; I will tell you some of my favorite bands, and encourage you to check them out and see how they can influence your guitar playing.

Tortoise
- http://www.youtube.com/watch?v=5sps7YxLeYM
Battles
- http://www.youtube.com/watch?v=1LLAN29W-4w
Zero 7
- http://www.youtube.com/watch?v=INn1C6ImJKg
King Crimson
- http://www.youtube.com/watch?v=yxoNjBujfkU
The Cinematic Orchestra
- http://www.youtube.com/watch?v=dvFiHvNsZLA
The Roots
- http://www.youtube.com/watch?v=qm7Xt2Qsjcg
Umphrey's McGee
- http://www.youtube.com/watch?v=6LyenwByWNI
Sly and the Family Stone
- http://www.youtube.com/watch?v=kjX2MKaZ-rg
Radiohead
- http://www.youtube.com/watch?v=Z9IODJdi3GA&feature=PlayList&p=F3E795907CFD3265&index=8
Sigur Ros
- http://www.youtube.com/watch?v=rCjjgDSJqUI
Gruvis Malt
- http://www.youtube.com/watch?v=vWcRAI5ne0M
The Bad Plus
- http://www.youtube.com/watch?v=sX_Iij8Eyts

Enjoy!