Download a free 46 megabyte collection of 728 synthetic drum and percussion sounds over at Cyberworm's blog. And if you enjoy the sounds, remember to donate to help ensure the blog goes on! Here are details about the material from the man himself:
"I worked on this samplepack for 2 months and finally did it! 728 single drums in one huge pack!
Samples made with Access Virus B/Virus TI, Jomox AirBase, Electron Machinedrum, Korg Prophecy, Polyvox synthesizer, Roland Juno-106 and "NoiseLab" drum synthesizer by Oleg Sharonov. Also used Alesis 3630 compressor, dbx 166XL, TL Audio Ivory 2, Izotope Ozone.
stick/rim/cowbell sounds: 68
wav format, 16 bit, 44100 hz, mono/stereo, 46 mb"