All I know is that I currently drive 124 miles 5 days a week in my v6 S-10 averaging about 22-23mpg which equals $440 every 4 weeks. (Not counting any weekend travel). I am doing some serious hybrid/economy car shopping. I still like the little Smart car so far, but I also really like the civic hybrid that I test drove. The Prius is in too much demand to be affordable right now.
some others that i'd throw out there for you (because I just did this recently) is the corolla, Camry hybrid, Civic, Civic Hybrid, Yaris.
i didnt like the Smart at all, drove weird and I felt like I could be killed at any time or that a big gust of wind might knock me over..
Loren on the forums here is getting 40+ MPG out of his Yaris, i am looking to get close to 40 with my civic this tank, corolla's regularly get over 40 and the Hybrids over 60. Any of them will more than halve your gas bill.