If you've ever pressed the "Get More" button from any of the preset browsers in Caustic, you'll have seen Audiovapor's kits. If you haven't taken the time to download the demos kits yet, I encourage you to do so right now.
Audiovapor has put together some of the biggest Caustic expansion kits you can find on Google Play and are offering them for next to nothing. The sheer number of PCMSynth and BeatBox presets contained in the "Substance" packs means you've got almost any style of electronic music covered. Each preset and kit was made and tweaked specifically for use in Caustic. I wish I had access to these when I first launched the app...
Check 'em out, there's a demo video showing them off on their website:
Audiovapor's Kits for Caustic