Since your two handheld meters give the same result they seem to be working fine. The fact your two in-camera meters give the same results also means they are working fine. How can they both be correct? You were pointing the cameras at something two stops brighter (like a white wall, or sunny window like you mention) and taking a "reflective" measurement, while the handhelds were measuring the "ambient" light (I guess they have a kind of diffuse dome on them).
To understand why, you need to know that light meters are calibrated against "middle grey" - a particular shade of 18% grey - thought to be average (neither too dark, nor too bright). White objects reflect more light, dark objects reflect less. The meter in your camera doesn't know anything about colours so it just assumes everything is middle grey. If you point it at a white wall, it will assume it's really a grey wall that happens to be illuminated by more ambient light. Point it at a black wall, and it's that same grey wall in a dark room!
So if you want to check your camera's meter you need to point it at a middle grey object, like a grey card. If you don't have a grey card, the palm of your hand, or green trees are said to be decent substitutes. Just remember to fill the frame with your grey card (hand, etc.) and you should get more-or-less the same reading from your handheld and in-camera meters.
See my answer to this question for more details:
http://answers.yahoo.com/question/?qid=20060920172713AAvkSMw
Just remember that photography is an art; so there really isn't any "correct" exposure. If you want to take a spooky Halloween photo, you may want to "underexpose" so everything looks dark and gloomy. Once you understand how your meter works you'll be able to have fun controlling exposure to get the creative effect you want!