A few days ago I got the Pacemaker plugin for Winamp, which basically lets you change the tempo, speed and pitch of an mp3. After a while of playing around with the settings, I found out that a lot of songs sound substantially better when sped up by around twenty percent or so, maybe moving up to thirty percent if needs be.

After a couple of test runs I found that some songs that were meant to be slow (for emotional purposes or whatever) don't sound that good when sped up.
e.g. Roads by Portishead or Full Circle by Aerosmith.

In addition to this, dance music doesn't sound that good, because if you already know the song, it sounds like it's supposed to be that fast.
e.g. anything by The Prodigy or Aphex Twin

Bearing this in mind, however, if you look for songs that thrive on their energy, then you're onto a winner :)
e.g. Chop Suey by System of a Down or Trip Like I Do by Filter and The Crystal Method

In short, the track only lasts eighty percent of the time it originally did, but the payoff of it is it seems the energy of the song is condensed.

Download the plug in from http://www.winamp.com