Rush - Xanadu. Talk about creating an atmosphere. Two minutes of nature sounds, auxiliary percussion and chimes, and gentle guitar noodlings? The whole song is blown wide open with the main riff in 7/8, with some impressive drum fills between each repetition. Then Neil Peart gets crazy with cowbells for a while just because. Finally the lyrics start five minutes into what is, in my opinion, Rush's best song.
Also, Yes - Heart of the Sunrise. Opening riff is great along with some hi-hat/snare paradiddles, but Bill Bruford's drumming during the slow section is amazing, and Rick Wakeman's synth-string pattern during the same section is just
so good, not to mention one of Chris Squire's best bass lines ever. Then Steve Howe comes back in with the main riff overlaid on everything else and it just builds and builds. Then you're thrown back into the main opening sequence again but the drumming gets more and more insane every repetition. Finally it all comes to a screeching halt right before the vocals come in.