So how did you like it? This was my second classical music purchase (the first was the 100 Beethoven tracks for $0.99) and it was all new to me. What tracks did you like the best? My favorite was the guitar concert from Vivaldi. I liked that type of relaxing guitar, almost like spanish guitar.
This is a decent starter, you can't expect to love or hate classical music based on five dollars worth of music. Piano concertos and concerto playing in general is good, however there is another side of the music that computerpro3 left out: symphonic repertoire. (I say that because I have a degree in bass trombone, and symphonies complete me, much like piano concertos do for you.
If you want to try something different, I saw earlier that someone asked about certain labels to listen on, deutsche grammophon is by far some of the best audio quality (and orchestral quality) that you can get. I have days of music on my hard drives, and the cd's that are DG are much more distinguishable than that of any other label (maybe bmg, cbs, naxos and telarc are close) even to someone who isn't trained to listen to classical music.
If you want to steer away from the baroque and classical music period, try some romantic music with Mahler, Brahms, Rachmaninoff, or Shostakovich (although he is modern). Mahlers second, and fifth symphony is some of the greatest music ever made (and is not just music for musicians).