It's ball pythons for me. ^^
As for tips and where to find the animals, that really depends on the area that you live and the type of animal you wish to specialize in. For you, cats and dogs would be easiest to find through local breeders (or maybe even a state or two away); look for ads, breeding associations, and forums.
Personally I like to use this website to find info and new animals (it's a forum system and classifieds all rolled into one): http://faunaclassifieds.com/
It mostly for reptiles, but it also has small sections for mammels, insects and arachnids, birds, fish and aquatics, flora, and "miscellaneous".