Hasbro, the parent company of Magic: The Gathering and Dungeons & Dragons developer Wizards of the Coast, isn't known for being the nicest company on the block. That said, it has been reasonably generous when it comes to licensing its RPG systems, with the d20 System Reference (SRD) and 4th edition Game System License (GSL) being notable examples. Now it's done one better with the upcoming 5th edition of D&D, providing the basic rules free.
OK, so you won't get a pretty book, but if you just want to roll up characters and get dungeon-crawling, then all you need are the rules in PDF form, which can be readily downloaded directly from the Dungeons & Dragons website.
Admittedly, it's not a trendsetter by any definition, but if you're happy to play with the basic classes (fighter, cleric, wizard and rogue) and races (human, elf, dwarf and halfing) and like coming up with your own adventures (or have a friend who does), you won't need to spend a cent. Of course, Wizards will still charge for supplements, such as more classes, campaigns and other materials, but in terms of business models, it's a step in the right direction.
For traditionalists, there's a $US19.99 starter kit that's set for release on the 15th, which comes with pre-generated characters and a campaign so you can jump right in. You can also expect in due course handbooks for players and dungeon masters, along with the requisite monster manual.
Image: Wizards of the Coast / Hasbro