I've used
Eagle before. It takes a bit of getting used to, and the parts library isn't quite as easy to use as I would like, but once you get it all set up it does autorouting quite nicely... but it is FREE.
The size of the PCB board is limited in the free version, but for simple circuits that has not been an issue.
Jason
P.S. I like the links provided here... I might check some of them out to see if they are easier for my students to use.