Enworld.org has a great overview of the various Old School retro D&D clones that are available, right now. Many are available for free as downloads (or for a cost in print format). If the current versions of D&D don't tickle your cookies as much as memories of the old boxed sets that required you ink in your own dice with a white crayon, then check this article out.
http://www.enworld.org/forum/columns/310462-retroclones-older-d-d-editions.html
