I mentioned SHERPA a while ago:
SHERPA is a large consortial UK project that’s attempting to build an academic archive/repository for 20 institutions, including the British Library and Cambridge University. [link added]
I bring this up again now because they’ve got some advice for people on the subject of digital archives. They recommend EPrints, an open source project developed and maintained by the University of Southampton. Second to that, or for those interested in archiving a broader variety of object types, they suggest MIT’s DSpace.