LilyPond looks like it'll be great, once I get the hang of its little notation language.
I've been avoiding my schoolwork by playing with LilyPond. Here's the first third or so of my piece from last semester, with lots of markings missing and some confusing notation, but enough to start playing through. I can safely say I really like LilyPond: even though I'm a beginner, it gives me as much control over the output as I feel like having. Neat software. And now I'd better get back to what I ought to be doing!
If anyone plays through this and has a hankering for the rest of the piece, let me know -- I'll be happy to procrastinate some more.