What's the best kind of monetary tip you and your band has received during a show - regardless if you set up a tip jar or not?

We played a gig last year where a guy walked up to our lead guitarist and asked us to play two Jimi Hendrix songs and two Stevie Ray Vaughan songs. He said he'd leave a tip if he liked it. During the middle of the fourth song he walked up and dropped four $100 bills and a piece of paper at the foot of our guitarist, then turned and walked out the door. He ended up being the owner of a local towing company and the paper had his name and number on it. We've played several gigs for his company when they do parties since then.