I've just come across a seriously amazing new technique for getting prints that look as good, and sometimes better, than injection-molded plastic.
It only works with ABS, so those of you who print with PLA - this won't help you any. Sorry.
Here's a couple of prints my buddy made and did this to -
Seriously! He printed those on a RepRap! You'd never ever guess it - no visible layers AT ALL.
Here's a video demonstrating the technique - the video is kind of crappy, sorry - hah. I've personally tried it and it's AMAZING how well this works.
Here's a blog post that explains the steps better than the video -
I also did my own using the technique which can be seen here: