Hilton is offering free gold elite status if you have a Visa Signature card... any Visa Signature card in fact. Just head to this link and enter your credit card number and you should be instantly upgraded to gold status through 8/31/2011. And if you accumulate 3 stays by 8/31/2011, your gold status will be extended until March 2013. The website is apparently a little buggy, so you may need to try signing up a few times before it works.
If you already have gold or diamond status with Hilton, you will receive 5000 points for signing up, even though these terms are not specifically stated on the website (EDIT: this bonus seems to have ended due to some people taking advantage of both offers within minutes of each other). Gold members receive room upgrades based on availability, complimentary breakfast, in addition to bonus points for Hilton stays.