This isn’t a new discovery, but I found myself recommending the Gentium typeface to someone this morning, and thought it made sense to post it as well.
Gentium is easy to read, especially when printed out. It can sometimes look a bit funky on-screen, but it has always held up for the final product. It looks a bit old-fashioned, but with modern touches. Best of all, it is open-source, so it can be freely installed on as many computers as needed.