Depending on how many doors need sprucing up and what your budget is, you can have art glass installed into your existing doors for a reasonable price. I've recently had my pantry & game room door updated with custom etchings, and my entry door updated with a beveled glass panel. Since you're putting glass in your existing door, you don't have to change out hardware or paint, etc. and get more light throughout the house.
You can do a Google search in your area to see what's available near you.
If you're looking for something to make it look a little nicer for a few bucks, I'd definitely go with "yummy mummy's" idea of the moulding to give it a nice raised panel look. It will be elegant looking, but very cheap to do yourself