My suggestion is two fold...

1) Practice the expressions that you want in the mirror. Make sure that you are by yourself (so people don't think your are crazy), and try to act out the expressions that you want. This is a time honored animator's technique.

2) Take pictures of your expressions and use them as photo references. A little more modern than 1) given the benefits of digital photography. Try to match the 3D character to your pictures as much as possible. Learn to use the auto timer on your digital camera. Some cameras will even take a quick 10 pictures in a row so you can simply pick out the best one. This works great for facial expressions with movement, like laughing, etc.

The same techniques work great for body poses.

As for all of the characters looking the same, you should look at these models as "starting points", and then morph/texture the heck out of them so they look nothing like the originals. You can get some great photo-references from http://www.3d.sk, however be prepared to see your share of naked old guys doing life poses :S. Personally, I just go for the head shots.

Hope this helps!
Konan