There are so many options for special offers you could about anything. The main purpose of doing one is to get your foot in their door. You could start with something small, like free window cleaning with housse wash. Or do an entire house wash at 25% off. I have also been thinking of running a special for residentials, but not really sure. I tried a special that said "Driveway cleaning only 99.00 and unfortunately didn't get a huge response. So like you Wade I would also like to know what works and what doesn't.
I know with commercial accounts I give discounts when they sign a maintenance contract and how often the want it done. I always include those in my bid package I send them.