Not sure how much money it'll net, but this is a good idea:

Want to make a few extra bucks from your wireless Internet access? Start-up LinSpot announced on Wednesday that their LinSpot 1.0 application for Mac OS X (news - web sites) allows you to do just that, with the company taking a 15 percent cut for services sold over your wireless network.

The best ideas are the ones that harness resources that are already out there, going untapped. Looks like a smart one.