Ordinarily, recruiting through your server's official forums is a good start. There are also WoW fan sites where you can advertise your guild, such as WoW.com's [The Classifieds]. There's also the method of running a lot of PuG raids (such as the weekly raid) to try to identify good players without a good guild. (Not everyone is satisfied with their current guild).
However, at this point during the game, you may find recruitment impossible no matter what avenue you use. Hardcore raiders and semi-hardcore raiders are pretty much done with all the content out there. "Hardcore" tends to mean progression-oriented, and there's nothing right now to progress through. A lot of people are even taking breaks from raiding or even from the game until the expansion.
I have two suggestions for you:
1) Wait until the expansion hits to start your guild. There will be a ton of new or returning players looking for a home then, and tons of new content to progress through.
2) Change your target audience for your guild. Look for people who haven't raided much and want to catch up before Cataclysm. This means looking for undeveloped talent, not people who already have high gear scores and tons of achievements. Invest in newbies or other players who haven't yet had a chance to shine.
: http://www.wow.com/category/the-classifieds/"The Classifieds"