At this point, cloning science is starting to get to the point where we can do some pretty solid stuff. There have been issues as far as cloned animals have decreased life spans but I don't much consider that a big issue, we only need them to be around long enough to breed. If we can clone one generation and get it to breed a subsequent generation then that species is back and we're good to go. This approach wouldn't work too well for wild species as there'd be no good way to introduce them into the wild in sufficient numbers to survive but I figure there're plenty of extinct animals that'd do mighty well in captivity. I'm sure that I could come up with others, given a bit of time, but here's a short list of a few animals that I think we should clone back into existence and why:
Dodo Birds: The dodo strikes me as an excellent alternative to chicken. The fact that they were dumb enough to stand around and get killed off by sailor means that they're probably dumb enough to be raised just the same as chickens. Additionally, they're larger than chickens--more turkey sized--and thus able to provide more meat. What is comes down to, really, is that I've seen stuffed dodos in museums and I think that the things look like they'd be mighty tasty.
Woolly Mammoths: Ok, elephants are totally awesome; they're giant, intelligent, hulks, capable of exerting incredible amounts of force and performing tons of work. Mammoths have pretty much all the advantages of elephants but they're also mighty cold tolerant creatures because of that whole ice age thing. So basically, what I'm talking about here is having elephants that you could ride around on in the winter. How awesome would it be to spend a weekend in New Hampshire, camping and riding mammoths around. The mammoths could carry enough stuff to live in total luxury and you could build a shelter on their back so that you could be out in harsher weather. I'm imagining having a mammoth gang and riding around the Midwest and Canada, kind of like the Hell's Angels, but with mammoths.
Pygmy Mammoths and Dwarf Elephants: Ok, having established that elephant like things are pretty keen, we should remember to bring back the varieties that were in the 4-8 foot tall range. Don't get me wrong, I love dogs; dogs are great, but wouldn't it be pretty damned sweet to have a little elephant too. I don't know what I'd do with one, ride it around, just play with it, I don't know but I think they'd make totally sweet pets.
Dire Wolves: You might be wondering why in the heck, I'd want dire wolves around again and the answer is that I don't. Why is it on this list, then? Simple, I want to infuse dire wolf genetic material into the modern canine gene pool. I'm really just talking about getting some very large canine breeding stock. Oh man, imagine breeding them with huskies and getting five foot tall sled dogs. Actually, this could probably be accomplished by breeding Timber Wolves with dogs; maybe we should just forgo the cloning and do that.
Elephant Birds: Gigantic flightless birds and I do mean gigantic, sometimes >10 feet tall and >½ ton. I don't really have any good reason or domesticable use for elephant birds so let's just go with because I think they're neat besides people could use them for whatever people use ostriches and emus for.
A discussion of cloning extinct animals because they're awesome wouldn't be complete without mention of dinosaurs so I'll just say that I agree with Jurassic Park; they are too unmanageable for zoos right now.