Unbelievably cool. Courtesy of Edge Studio's Voice Design Group  there's a place for voiceover folks to view and have free use of practice and demo scripts. 

This resource is excellent  for working on copy privately or  to print and take with you to voice workout classes.

Unlimited, free access to over 3,500 commercial, narration, and specialty scripts.
Alphabetized, updated, and organized in 21 categories.

Personal Note: If you're thinking about the use of any script for use on a demo make sure the script/product you select is timely and not something that's no longer available or applicable to the current marketplace. (like the "all-new 2007" car, for example.) I also think in commercials, you won't want to use too much, if any product brand name dropping, because an employer of a competing brand may view that brand identifier and your voice as a conflict.

I feel it always makes good sense to change the copy slightly to make it your own.  And if you do use anything from the scripts available on your own demo, there is always the risk of doing the same thing somebody else selected to have on theirs. Better yet...look at the ideas there, pull some ads from magazines, and write your own.

For a voice demo, I have learned, it's the read, not the product that's the centerpiece.

Have a happy, fun & spirited Halloween!