To clarify, I don't currently run any Windows environments, so Linux or Mac suggestions are perfect. 
And wow, thanks for all the discussion so far. I was kind of expecting this thread would be one of those classic Bar Sport flops that gets two half-hearted replies, but here it is ~24 hours later and we're on page two already. I have a lot of research to do!
Has there ever been a poll or other attempt at gathering info on what software hobbyists use? I've used EAGLE to date purely because I perceived it as the most popular, and since I'm interested in working/sharing with others, it's important to me to work in a format that's as universal as possible. But here in this thread I see more non-EAGLE users than I'd expected. . .