If you've ever had a car that's not so new, you know what a hassle it can be to try and get an honest opinion of why "Check Engine" keeps popping up. Now, as long as your car was made after 1996 and was sold in the U.S., you can check the problem yourself with CarMD ($90). Simply plug CarMD into your car's Data Link Connector and start the ignition. A series of beeps tells you when the testing is done, and if you have a yellow or red light, you can hook it up to your computer and download a detailed report of your car's problems, complete with service estimates. Sure beats paying some grease monkey to replace something that wasn't broken in the first place.