My son is fond of his scotch tape. He wanted a dispenser since the refills didn't fit in his old one.
The openscad file is somewhat parametric but is untested it with any other settings.
It uses syvwlch's awesome thread library ( http://www.thingiverse.com/thing:8793 )
So, you'll need that if you want to use the scad file.
There are two versions. One has a slot to insert a chunk of the metal blade from a plastic wrap container (or foil or wax paper...).
I have redesigned the plastic blade so that it works pretty well. It doesn't make quite as clean a cut but it seems to work fine (at least from my printer with a .2 layer height).
If you print out the one with the slot for the blade, I've found that it seems to work best if you bend the blade so that it is pointing away from the roll after you stick it in the slot (and glue it).
If you are going to compile it yourself, download the thread library (http://www.thingiverse.com/thing:8793) and put it somewhere on your computer and change the scad code to reference the correct location of the Thread_Library.scad file.