DVE doesn't have any kind of gamma reference, and the only real way to properly adjust gamma is with a meter (like the SMART III system). Avia, however, has a gamma pattern that works fairly well for getting it close by eye.
In very simple terms, gamma is how quickly the white level goes up in relation to the supplied signal. If the IRE levels above black (0 IRE) look too dark, you lose shadow detail. Raising the gamma level alters the curve by which each IRE level goes up in contrast. In other words, it isn't linear; 10 IRE does not equal 10% gray. Without Avia or a meter, all you can do is just adjust the gamma setting and see if it brings out the shadow details better without washing out the picture.
As for The Ladykillers, The Village, etc. this is because those movies are 1.78:1 instead of 1.85:1. Put simply, the black bars to the side are encoded on the DVD to keep the picture at the proper aspect ratio. The reason most people don't notice this is that most people have a certain amount of overscan (usually around 5%) that conceals the black bars on the side. So if you really want to get rid of the bars on the side, just increase overscan. You'll cut off a bit of the top and bottom of the picture, but not so much that you'll miss anything.
There are many DVD's that people consider visual references, but it's pretty subjective. The only two that immediately come to mind for me are The Fifth Element: Superbit (which is good for checking fleshtone delineation and detail) and Charlotte Gray (which just has a damn nice transfer). Another one that I like that looks so good it seems hi-def is the haunted submarine movie BELOW, which is also very good for assessing shadow details.
"Never believe any quote you read on the internet." - Abraham Lincoln