Wizards of the Coast announced today that it's now offering a huge pile of 80 Dungeons & Dragons core rulebooks, sourcebooks and modules/adventures/campaigns, all available as high-quality freshly scanned PDF downloads from a Web catalogue. Eventually, there will be hundreds of books available, including some that are from back in the 1970s and 1980s and bascially impossible to find anymore.
Unfortunately, this isn't a giant free catalog: all of these PDFs cost money, generally somewhere between $5 and $10, although the core rulebooks can get up closer to $20. It may be worth it to buy a physical copy of your core books, but for quick access to new campaigns and stuff, an easily downloadable PDF that costs more than an evening's worth of unhealthy snack food is a no-brainer. Plus, having a digital edition means you can easily search the damn thing, saving hours of fruitless page turning.
I have to confess, though, that back when I had to buy three wolf moon shirts in kid sizes and not adult sizes, I was way more into GURPS, which I still think is better than D&D in a lot of ways, especially in terms of skill points and modeling weapons and armor in combat. Aaand I've probably said to much. Um, I'm going to go drink beer and play football and watch wrestling now and not go browse the D&D catalog. Because that's for nerds.