The release canidate version is a version of the game that the developer sends to a publisher. If the publisher thinks that it is worth of being the final product, the software will "go gold" and the game will start to be made. If it is rejected, then the developer has to go back and improve the game. IIRC the developer of HL2 (Valve) just recently sent in another release canidate, don't remember if it went gold or not though.
That is the problem with this. I remember false "going gold" news stories, and various release date things, and they all get jumbled up in my head to the point where now I don't know what its status is...