I just got in from the YES concert down at Shoreline Amphitheatre (Mountain View, CA.). It was an awesome show!  
It's amazing because these guys are in there late 50s and there music is very complex un-like many rock groups . They have been around since 1968.
I have been a fan of YES for almost 20 years and have never seen them live until tonight. They are one the better bands from the United Kingdom and are very talented. If you are in to 20 minute long art rock songs, they are the band to check out if you haven't.
There album covers are great also. Roger Dean does the artwork for most of their LPs.
My favorite member is Rick Wakeman who plays the keyboards. He even had his analog synthesizers like the Mini-Moog and Clavinet as well as displaying his organ.

For those who don't like YES may want to check out this album.