Edmunds has done a study to determine which hybrids will allow you to recover the hybrid premium in fuel savings the fastest. Anything that will allow you to recover the cost within five years makes sense financially. Most interesting is that the Prius is a bad financial choice, taking 13.6 years to recover the price difference between it and a Corolla if you drive 15,000 miles per year.
When compared with small conventional non-hybrid cars, no hybrids are fost effective within five years unless you drive 25,000 per year, and even then the Prius fails against the Corolla, coming in at 8.2 years to break even.
You can read the results of the study at http://www...ticle.html
It looks like it will be some time before Hybrids make financial sense.