AdoptMe.com is a free virtual pet site and is one of the most popular. Although it doesn't have the '3D' effect of the Foo Pets game and is more cartoon like, AdoptMe.com still provides you with a virtual pet and a virtual world for both you and your selected cartoon pet. You can train your hamster in a gym, race your horse on a track in a competition, take your pet to a vet who will take care of your poorly animal and play baseball in the park with your snake. AdoptMe.com is very extensive for a free virtual pet game and is a brilliant choice if you're looking for a fun and entertaining virtual pet game for free.
Mara Pets is another free virtual pet website but is slightly different to AdoptMe.com. It invites you to adopt virtual pets from a 'pound'; this is where other players have abandoned pets they can no longer care for or no longer want. As soon as you adopt one, that pet is your responsibility and you can then log in to enrol your pet in school, train them in the gym, breed them, get them a job and treat your pet to some treats by going shopping.
Other websites that offer a free virtual pet game that requires a simple registration and no payment are Powerpets.com, dressupgirl.net (Animal Games section), Guffins.com and Minimonos.com.