You will find that everyone differs on this subject. Some give full resolution, some give email/web sized, some refuse to give them digital negatives (digital pic files)period.
For CD/DVD's I give full resolution
I personally give them to the people (sometimes) and my charges range depending on the job. You ultimately are the one who has to decide what your skill/equipment/time is worth. I have charged as much as $50 for one file on the other hand when I did a fund raiser for my son's baseball team I charged $50 for a disc with all the pics from a weekend tournament and then gave $20/disc back to the team for entry fees uniforms or whatever the team wanted to use the money for.
Look at these links they might help also.
Link 1 Link 2
Hope this helps and welcome to TPF