sparkfun.com has a great tutorial series on using eagle from cadsoftusa.com
for simpler projects, or just drawing up a quick schematic for discussion here, expresspcb.com has a simple to use tool.
others prefer kicad, and fritzing.org seems to be showing up a lot, altho posters here can't seem to get a usable schematic for posting here for any kind of design review discussion.
prefer sending gerber files to a place like iteadstudio.com, ten 5cm x 5cm double-sided boards, soldermasked, silkscreened, $10 plus shipping from China.
Folks also make their own, good for one-off designs. I'm not gonna be bothered with drilling all the holes for thru-hole designs and populating vias for SMD's, etc., not when I can get professionally created PCBs for so little money.
Another site was linked here recently for similar service, 3 boards, 2 square inch (or 2" x 2"? not sure now), $5/sq inch. I''ll repost when I find the name.
I've done quite a few boards and usually have bare boards available to sell for pretty much cost plus mailing:
www.crossroadsfencing.com/BobuinoRev17