I just learned (well not really, I've thought about this before) of a more efficient way to clean up drawings. Rather than doing a rough sketch, scanning, then spending a really long time (possibly hours) tracing the drawing in Illustrator or Flash, I tried drawing using a blue col-erase pencil, then tracing it over in pencil. After scanning, and channel subtraction in Photoshop (or any other graphics program), it'll give you a perfectly clean drawing. Here's an example:
The original drawing:

Blue channel isolated in Photoshop:

(Don't mind the crappiness of the drawing; I did it in a couple of minutes, and I'm not that good at tracing yet)
I know a lot of people probably already know this, but this is the first time I've tried it and I'm very pleased with the results. The only other way I know of cleaning up drawings is by using a light table, and that's not very convenient. And of course, there's also doing it directly on a computer, but that's very tedious.