Relmstein has a great tongue-in-cheek guide up about how to "poach" great raiders for your guild. I'm assuming that he doesn't actually suggest you start stealing raiders from other guilds (unless you want to show up in Guildwatch next week), but not only is Relmstein's writeup really funny, but there are a few actual suggestions hidden in there about ways to promote your own growing guild legitimately.
Now, you don't want to start lying about how Eyonix is your GL (#7), or stand outside Karazhan trying to show off (#4), but there's nothing wrong with making sure people know that you're progressing. Have your guildleader post on the forums when you make a big kill, or throw out a few yells when you're about to give out a zone-wide buff (I remember when my guild turned in the Onyxia head way back when, and we did a nice parade through the center of Orgrimmar, all decked out on our mounts). A great video helps, too-- a funny recruitment video will get you attention, but a how-to video for a tough boss your guild has on farm will attract exactly the kind of people you want on your team.
You should never try to steal raiders from other guilds-- guildleaders have a hard enough time keeping a raiding team together as it is without teams fighting amongst themselves for players. But there are always good ways to "advertise" your guild to the right people, so that when a good raider is looking for a place to hang their hat, you can make sure they find you.