Begging for Boobies
Get permission from local authorities in your town to block off an intersection and stand in the intersection with pink buckets (sort of like a fireman's fill the boot fundraiser), and ask passers by for donations.
We were supposed to have a car wash and it rained, but we didn't let that stop us. The day before we called the town hall and double checked that we didn't need any permits, and kept the same location as the car wash (a local firehouse).
The captain of the firehouse dressed in his gear, and blocked off the road just at the intersection and held pink a pink bucket. While 3 of us 3-Dayers and one very enthusiastic youth corps member stood out on side of the sheet thanking people and also had buckets out.
We raised nearly $1100 in 3.5 hours. We averaged about $300 per hour, so it was a very successful fundraiser.