For a single Benjamin Franklin bill (hundred that is), you can pick up the CarMD Handheld Engine Code Reader that interfaces with your car's computers to tell you what's wrong with your car in seconds.
This little gem works with all 1996 and newer model cars and provides complete diagnostics on your car's engine and whatever else your car's computer tracks. CarMD comes with Windows software that helps you track up to 3 of your cars' health. In addition,the website www.CarMD.com has an online database of thousands of problems and their solutions as seen by auto techs over the past 10 years.
Naturally, it has a USB hookup to your computer for easy connectivity and data dumping. If you've got a car that gives you any sort of trouble, or you want your very own second opinion, in this time of rising gas prices, then this gadget may just pay for itself the first time your mechanic tries to hoodwink you.
(Please note prices are subject to change and the listed price is correct to the best of our knowledge at the time of posting)