There are quite a mix of breeds that they use for these sniffers.
One officer had a pitbull/hound mix, one had a border collie, one had a border collie mix, there were labs of all colors, German shepards, but what we saw the most of were the Belgian Malinois...this page will tell you about them. :)
http://www.dogbreedinfo.com/belgianmalinois.htm