As stated above you'll need a code reader, personally I would tell the wife I need the superchips or hypertech and not say a damned thing about a scanner. If you do opt for a scanner you can pick one up from auto zone or the likes it just has to be an OBD III reader I do believe.
I haven't had the check engine light on in a long time but I know if you hold the trip/reset button while you turn the key to the "on" position and then let go it will test all the gauges. I don't know if it will tell you what the code is. I always use a snap-on scanner.