How old are the kids? One thing that I am working on right now is getting some merchandise/memorabilia from a local band, MxPx, and then we will do an ebay auction starting on the release date of their new album, July 17th, and so if you can utilize the youth at the community center to write letters to the managers or the record label, or through their favorite bands "official websites", then they might be able to obtain these items. Another suggestion would be to have them organize a talent show, or comedy night, or get a local band to do a benefit concert. If they are old enough, another one would be a neighborhood "mow your lawn" day, i.e. distribute fliers in a large neighborhood and advertise that your crew of teens will be there on X day, ready to mow lawns for a donation (minimum donation of $ X, but more will be accepted because all proceeds go towards our playground)... then have a way for the homeowners to signal that yes, they want their lawn mowed--either give them a brightly colored flier and instruct them to tape it to their front window to signal the lawn-mowing crew.
If the kids are younger (i.e. not teens) let us know and we can brainstorm other ideas...