I don't believe straight gasoline powered vehicles ever qualified for the original tax credit which is no longer available on cars like the Prius, etc. since they've reached the cap. Cash for Clunkers was $4,500, but this credit topped out at $3,400 I think depending on various factors. Some states may offer a credit that is separate from the federal credit, but that depends on the state. See the following article for a little more info:
No tax credit for Prius, but other hybrids eligible
As you would suspect, Toyota sells the most hybrids, so that company was the first to end tax credits. If you bought a Toyota Prius before Jan. 1, 2006, the tax credit was $3,150. But later that year, Toyota had sold 60,000 hybrids, so the Prius credit dropped to $1,575, then $787.50, then -- after Sept. 30, 2007 -- nothing.
If all these incentives don't sound particularly fair, well, they aren't. The Smart ForTwo, for instance, is rated at 36 miles per gallon overall, but since it is powered by a regular gas engine, there are no incentives offered for it. But those Chevrolet Tahoe and GMC Yukon hybrids, rated at 21 mpg overall, have that $2,200 tax credit.