06 Acid Acid has beat-matching and tempo-detecting facilities and is designed for a cut-and-paste style of music making - more about editing and arranging samples than creating new loops.
So breaks merchants and hip-hoppers will find it useful and you can definitely have some fun with this and the 1XMusic Sample Bank.
It comes with a few synths and drum machines so you can add your own parts alongside the samples.
You can add even more using plug-ins (see the section on these at the end).
The full version is fairly pricey - about £225 - but there are two cheaper options offering fewer features for the hard of pocket.
It integrates well with other software, so you can take it with you if you decide to move on to a system more suited to recording song-based music.