I think the next piece, suggested by the Evil Mad Scientist himself (whose evil I seriously doubt. he seems quite nice, actually), is a serial listener that runs on a PC. He suggested writing it in Processing, and mailed me a program that works but isn't very flexible. It's a good proof-of-concept, though.
Ideally, it would detect serial ports and display a menu to let the user pick an active serial port. (Right now it's hard-coded.)
It should also let the user pick sounds for slots 1-8. Since they don't have to be copied to an SD card here, they don't need to be renamed. Especially since, if we're on a PC, we have all kinds of memory and CPU to play with and don't need to take the string-crunching shortcuts I took in the MeggySeqListener arduino sketch.
If I get enthusiastic, I could even have it copy the files to an SD card, or to a directory or something, and rename them correctly and stuff. But right off I think the easy playback (for people who have a Meggy and don't have a Wave Shield and so on) would be a big help.