make sure you get a decent website up for contact, let your alumni gather information from the site on their time and contact each other too.
Websites and forums are huge tools now to get and maintain interest. just MAKE SURE TO UPDATE IT!!!
nothin's worse than lookin for info on a chapters site and reading
"Last update : October 31, 2001"
you can imagine how that reflects on a chapter as opposed to say, Lambda's website, which if you haven't seen, is just amazing...
http://www.sit.wisc.edu/~tke/