Haha that's a bit of a vague question! What are you looking for in a pet?
That will help people narrow it down.
Personally, I'm a lover of Russian dwarf hamsters - both Campbells and Winter Whites. They are friendly, easy to tame (for me, at least!), cute balls of fluff!
They come in a variety of colours, get along well with their own kind (particularly Campbells, and especially those that are well bred), and are rewarding little critters to own.
You can keep 1 or 2 Russian dwarf hamsters in a 20 US Gallon tank, nothing less than about 30 x 12 inches. They can also have bin cages or wire cages or wooden cages of this size. For 4 hamsters, you'd need about twice that size more or less. Try to avoid huge colonies, or groups of three, as fights are more likely to break out. Each hamster needs a 6.5" (or bigger) wheel and a place to sleep/hide. You also need at least one water bottle per 2 hamsters, and a food dish big enough for all of them to fit in - or you can scatter feed. They need Aspen wood shavings, not Pine or Cedar, or some other substrate; the deeper the substrate is, the better. Toilet paper can be given as nesting material. Aim to clean out the cage every one to two weeks. They need clean fresh water at least every two days, and Hazel Hamster is the best food for them.
That's pretty much everything, they're amazing pets and easy to keep when you know what you're doing
They're not for everyone though, so you might be looking for something completely different!