Since some of you expressed an interest last week in laying your hands on Basic D&D so you can kick it old skool with your own bad selves, I suggested that you take a look at Labyrinth Lord. While you can get (possibly even legal) PDF scans of Basic D&D from RPGNow, which is where I got what we were using, you’re paying $5 for a not-particularly crisp scan ($10 if you want Expert as well). Labyrinth Lord is essentially Basic & Expert D&D as one book, released under the OGL as a free download. The rules themselves are the same, near as I can tell (with a few fiddly exceptions like rolling 3d8*10 for starting money, and Clerics being able to take spells at Level 1). All the text has been rewritten with an eye towards making it available under the OGL without it being in any way encumbered with any TSR intellectual property that hasn’t been explicitly released by Wizards of the Coast under the OGL. As a practical matter, the rules appear to be interchangeable, with only the organization and some minor terminology changing (e.g. Save vs. Dragon Breath is now Save vs. Breath Attack).
update:By the way, if you do decide you want to buy a pdf from rpgnow, you should probably get the D&D Rules Cyclopedia, which is the same price as either of the other two ($5), but has all the rules that were published for all the boxes: Basic, Expert, Companion, and Masters. What it lacks (the long introductory solo adventure and beginner dungeons), you are unlikely to need.