Pet Battle Teams allows you to form teams that you can load up with a click. The interface is a little awkward in that you can accidentally overwrite any team as long as it is the one highlighted, without confirmation. Right clicking on the team will delete it, but a confirmation dialog does popup for that. Otherwise, whatever team you have loaded in your journal will determine whatever team is highlighted.
I find Pet Battle Teams extremely useful for both leveling pets and collecting them. Don't judge me on the levels of my pets. You see, I've been collecting rather than doing the pet battle quests. I want to be the girl with the most rares.
My favorite of these add-ons is Pet Caught. With it installed, mousing over a wild pet indicates whether you have caught one before. If you have, the mouse-over tip tells you the highest quality of the pet in your journal by both word and color. Mousing over the green pawprint in the minimap shows the same information.
When I am out pet-collecting, I now don't have to check my journal every time I come across a wild pet that I may or may not have a rare of. Pet Caught is a real time-saver.
Do you have any more pet battle add-on recommendations? I'm always looking for more to test.