The current edition is the 4th edition. You don't necessarily need adventures, you could prepare your own, I never bought adventure books. In theory, yeah, all you need are the DM's guide, Player's handbook, and Monster Manual. There are countless different roleplaying games that exist nowadays too, and are quite popular in the gaming community.
Some of which are legally free:
Dungeon World: A more free-form RPG, it's free, but you can also buy it as a book or a PDF I think
Fate Core: An even more free-form RPG that can be used with settings other than fantasy. This game was kickstarted and the books can be bought in store, but the game is also free online.
Labyrinth Lord: Same deal, is free but can also be bought. This game is a lot more "classic", if you're adamant on looking for that old school 80s feel, this might be where to go.
If you really absolutely need to play D&D, I would wait until the second half of 2014, when it is widely believed the new edition of Dungeons and Dragons will come out. It attempts to take modern D&D a bit back towards its roots, to some extent. The currently available 4th edition may or may not be to your liking. It has more videogamish elements added into it, which may not be a bad thing, depending on how you view it.