There is a good chance you have already found out about WotC rereleasing many classic D&D PDFs, so I won't pretend that I'm breaking any news here. Of couse, if you haven't seen them yet, you should browse over and take a look:
The servers seem to be under some strain though, so you might want to come back in a few days after the initial stampede.
I haven't bought anything yet (I'm just settling in from a transatlantic flight), but I'm sure I will. The PDFs for sale now are from recent, higher quality scans, and are bookmarked (according to the product copy I have read).
Thank you Mike Mearls and everyone else at Wizards of the Coast that was involved for making this happen. Moldvay D&D is now in print again, and for only $5!