In December some friends and I hosted a guest bartending fundraiser at a popular bar in San Francisco, CA. In large cities you might be lucky enough to find bars/restaurants that open up their businesses to do something similar. Essentially, during a low traffic period of time (in our case, a Saturday from 6-9PM), you and a group of friends can go behind the bar and make drinks, and all tips (possibly both cash and credit depending on the business) will be pooled and donated to your initiative.
Depending on how well you advertise, you can make anywhere from $100 - $2000 dollars. On top of the tips earned, another volunteer and I donated several items to be raffled off, mostly a bunch of leftover souvenirs from Nepal. The more people drink, the easier it is to get them to buy raffle tickets ;)
I organized the fundraiser in conjunction with a friend also raising money for a volunteer trip to Peru. After splitting costs, we raised around $400 for Conscious Impact.