Propellerhead Software's ReBirth was the first software synth I ever heard that really impressed me. It's great fun to play with, and you can download it for free from here. Here are some of my Rebirth tunes.

Sorry, what I meant to say was:

HeRe aRE sOMe aCiD trAXx FRum dJ MarKALoid!!

Song 5 (1819K mp3)
Song 7 (1696K mp3)

Music for Robots