Democrats are lacking good slogans that resonate with the populace and provide effective repetitive sound bites. A good slogan should both support the Democrats policies and put the GOP into a defensive mode. It should be a point you can keep coming back to and hammer home.
How about...
Bush spent your tax cut.
It's simple, it fits on a T-shirt, and explains why we cannot afford to keep low taxes on the wealthy. It also makes for a good rant.