Cash for Clunkers?
 

No it's not a program yet... but it was actually introduced and, if passed, would be a way to get credit on a used hybrid:

See:

http://www.networkworld.com/community/node/37337

Since the program would be a tax credit, I doubt many people would be able to get the new hybrid car tax credit *and* a cash-for-clunkers credit on the same car (many people can't get full credit for just one tax credit due to the alternative-minimum-tax rules). But so far there's been no way to get a tax credit for buying a used hybrid -- it appears that this measure would change that.