There are no genetically modified squirrels. The GM salmon was recently approved by the FDA and is the first GMO food animal to be approved. The salmon was genetically modified for a few reasons including conserving wild fish populations and providing low impact aquaculture. Read more about this first GMO animal, why and how it was created.
As for other animals, you may have heard of GloFish® - check out their website for more information on these commercially available fish.
The use of genetic engineering is an exciting technology with a lot of potential for scientific advances, but as with any new technology it requires a lot of discussion and a good reason - besides the cool science - to do it.