Tim Cutler has put together a nice database of various harmonic progressions that can be used to supplement music theory textbooks. I've added it to my list of music sites to the left. Music students might enjoy looking up examples of V progressing to IV or Parallel voice leading as means of flustering their theory teachers. "But Brahms moves from V to IV in m. 88 of his Violin Sonata no. 2, 2nd movement. Why can't I?" Interestingly, Brahms wrote a monograph called "Oktaven und Quinten." It was a collection of parallel fifths and octaves that Brahms had found in works of the tonal masters. Heinrich Schenker published an edition of this monograph in 1933, using it to show how his theory of structural levels explains away the parallels as foreground phenomena mitigated by the underlying middleground (deeper structural levels).
You may enjoy looking through and listening to the various examples of the database, especially if you have studied or are currently studying music theory.