Call me an oldies snob, but the first disc of Chicago, titled The Chicago Transit Authority (their name before they were threatened of legal action by the actual transit authority of Chicago), is top-notch music. In it's early days, Chicago was distinguished by its distinctive sound, being essentially a rock band with a brass section, and are still around nowadays, but their music became progressively worse since the first albums. I couldn't find everything I wanted on youtube, though.
Listen - My favorite. It starts with a prolonged guitar note while trumpets blare, and mantains the tempo throughout the lyrics, solo, and ending. It's just a nice song.
I'm a Man - Damn this one's a hell of a ride. At first, only a guitar strumming, but then it's joined by the drums, maracas, and other assorted instruments and the crescendo continues until the song begins. It features an awesome drum solo in the middle and it ends with a bang.
South California Purples - If you love guitar riffs, then you'll love this song. A heavily distorted riff serves as the background for this song, which has a unique feel.
Prologue (August 29, 1968)/Someday (August 29, 1968) - There's someone shouting through a loudspeaker, and then a crowd starts chanting "The whole world is mine! The whole world is mine!" until a guitar interlaces with the chants. It's a politically charged song. And it's awesome, too. The song ends at around the 5 minute mark but for some reason the video doesn't end until almost 9 minutes.
Of course, if you don't listen to anything made before the 80's you wouldn't like this. I also wanted to put "Liberation" on here (15 minutes of guitar rocking!) but I couldn't find it.