We have done these before.... just a few ideas.
1.) We rented 2 50" plasma screens that ran commercials. These seemed to draw the people closer to our area so we could try and start the sales pitch :) If you want a commercial made I have a close personal friend who did ours. PM me.
2.) Try and have at least one computer that is connected to the internet so you can sign people up on the spot. You cant trust that people will go home and do it themselves. Have a nice printout made for them with tips on how to use their account.
3.) Make 1000's of business cards that are actually a little flyer. We got double sided full color printed from
www.gotprint.com - we went through about 3 boxes of 1000. Pens are also a great giveaway.
Hope this helps. If you have questions just post them :)