Probably not what you're looking for, manning, but these (standalone) drum sequencers do a rather good job:
http://www.threechords.com/hammerhead/hotstepper.shtml
The HotStepper's development has stopped, alas, but you can dowload the latest version at the dev's site:
http://www.hotstepper.de/Hot203f.zip
Loads and saves .wav files. (no MIDI)
I made a screenshot:
http://stashbox.org/uploads/1158105073/HotStepper.png
http://tnikolai.nm.ru/drumflow.html
DrumFlow is really good MIDI drum sequencer; connect it to REAPER by means of a virtual midi cable. Features and screenshot here:
http://tnikolai.nm.ru/df-features.html
At least these 2 won't cost you a dime - but again, it's not exactly what you're dreaming of