Giga Pets Plus
Giga Pets Plus was the second wave of Giga Pets released in 1998, and both featured multiple pets in one device, as well as voice (or sound, really) recognition.
Giga Farm
Features a Pig, Sheep, Cow, and Horse.
You grow crops and care for your animals (you can raise all 4 at once) , making it a far more involved pet than previous Giga Pets!
Giga Pound
Giga Pound features 8 different dog breeds, and you can raise up to 4 at once. This one does not have anything else to manage, unlike the Farm, but is still cute!
Looney Tunes
Bugs Bunny, Taz, Daffy Duck, and Tweety are the four characters you start with, and Yosemite Sam and Roadrunner can be unlocked as you play. None of them can die, but they will leave if the score drops too low.
Giga Circus
This is one of the rarer Giga Pets, and features a total of 7 animals you can raise: Lion, Sea Lion, Elephant, Pony, Tiger, Monkey, and Bear.
Giga Rugrats
Take care of Tommy, Chuckie, Spike, or Angela. The instructions are written from Tommy's perspective as well, a very cute touch! They work similar to the pets, where they'll leave after 14 days unless your care is very good.
Giga Small Soldiers
A very unique pet, probably really trying to market towards boys. I don't know the franchise, but apparently they have a "shelf life" of 14 days and they don't die - they explode.