So, I'm not a Sig, BUT my boyfriend was Recruitment chair 08-09, and Consul 09-10 so I think I might have some good ideas
I've thrown together a list of things they do that are successful:
1. Wing nights where they hang out and watch football games. Usually they're able to reserve a room on campus and get wings catered for that.
2. DODGEBALLLLL. Always a hit. They reserve one of the gyms on campus.
3. They try to do events with a few of the sororities, but I'm not sure if that's allowed where you are.
4. Attend a University sporting event... football game, basketball game, etc.
5. Capture the flag/flag football/kickball/wiffleball etc etc etc
6. One year they did a community service thing as a rush event. That'll make sure you're getting quality men too.
If its an event that doesn't allow for much talking (like dodgeball), allow for some of that at the beginning or end, like have some food for afterwards or whatever.
At all of the events (except rituals I guess) they allow sweethearts, and at some of the events they allow girlfriends to come. Having girls there talking to the PNM's allows for a different point of view on each of them. Also, guys are usually more willing to open up to girls, and girls can read people better. There also may be a list of ways to advertise on campus on your school's website (I know there's one for my school, at least). Definitely look into that.
Bottom line: make use of your university's resources, and have events where people can have fun!
Hope this helps a little