Trackers

Acid Pro
Loop based music creation tool.
http://www.sonymediasoftware.com/Products/ShowProduct.asp?PID=928

Atomix Productions
Offers Virtual DJ, DJ Box, and AtomixMP3 programs.
http://www.atomixproductions.com

Hip Hop Starz
Make your own Rap and Hip Hop. 1100 samples and loops for constructing your tracks.
http://www.hiphopstarz.com

Jackson, DJ
Mix any style of music and change the structure of songs while you're playing them.
http://www.jacksondj.com

Magix Music Maker
Sample based music creation, also templates for making musical websites and videos.
http://www.magix.net/

Samplisizer
Create music in modern club styles. Demo available.
http://www.overgamer.com