Just popped this one in for a first listen....
On the second track....different but really really cool so far...
Starts out like a Pink Floyd album, with guitar riffing that even seems a bit Gilmouresque

The Mars Volta - Amputechture
Edit: This is a dense listen, like all their 3 albums, however, this one *may* be the most accesible, maybe not, depends on what one thinks is accessible. Pretty complex in time signature, but not pretentious like a lot of 70's prog.