This promo started yesterday, but just in case you didn't know about it yet:
Fileplanet.com is currently dispersing a set of beta invites for Final Fantasy XIV from August 12 thru August 16. The catch is you need to be a paid subscriber to be eligible, with the lowest plan set at $6.95; you can cancel anytime however.
Also note the keys Fileplanet is distributing are for North American players only.
Once keys for a particular day have been exhausted, you will have to wait and try again on the following day.
If you're a bad enough dude to pay to play for a beta, here's the URL:
http://www.fileplanet.com/promotions/final-fantasy-xiv/(Remember, these keys are currently selling in the ballpark range of $100~ on eBay)
Protip: The current trend seems to be that Fileplanet will push their next batch of keys at Noon PST, but keep in mind they wish to keep the contest as "fair" as possible, so there is a probability of them randomly changing up the hours to keep everyone on their toes.