Share 'ONLINE RESOURCES: What are you using?'

I think it would be very useful for people to contribute information about online resources they use for post-classical texts - preferably text files, but also PDFs, scanned books, etc. There are probably hundreds of online medieval Latin books that I make use of right now, so I'll try to be good and post 5 items per day for a while here until we get a good pile going - please chime in!!!