If it's a purebreed, it should be recognized by the American Kennel Club - here's the link to the breeds sorted by groups.
http://www.akc.org/breeds/recbreeds/group.cfm
There is history and information about all breeds, and pictures.
Even if the one you saw is a combination of breeds, if you browse around you can probably recognize some traits, and you might see one you like even more!
If it's a small dog, I'd recommend starting in the Toy or Terrier groups.