I was searching for information on LINJ, a Lisp language that compiles into human-readable Java code. Unfortunately, the LINJ web site http://www.evaluator.pt/linj.html, is currently offline.
Luckily, it turned out that the Internet Archive Wayback machine had cached both that page, and the download files that that page had pointed to. Very cool!
Similarly, I was looking for the source to the Windows CE port of Quake 3, and found that the project's web site http://www.noctemware.com/q3ce.html had been abandoned and taken over by spammers. Luckily the Wayback machine had cached both the original web page and the downloads.
Let this be a lesson to you aspiring open source developers out there: It's better to store small open-source projects in a large "won't-ever-go-away" source repository like SourceForge or Google Code than to use your own vanity domain hosting. Of course, even using a large popular repository is not failure-proof. Some large code repositories from the early days of the Internet, like DEC's ftp site, have gone away after their owning company was bought by another company. Perhaps some sort of distributed system of discoverable git repositories is the answer.
In the case of Quake 3 for Windows CE, I've contacted the author, Christien Rioux, and with his kind permission I've set up a code.google.com project so that other people can more easily find the sources (and binaries): http://code.google.com/p/q3ce .