There's a really interesting article in November's issue of Nature. The author Henry Nicholls answers the question what would it take to clone a mammoth. This is more of an intellectual exercise than an actual doable process at the moment, but only because they don't have the entire genome of the mammoth sequenced yet.
I was very impressed with the detail and clarity of the article, it brought up questions that I never considered. When making a mammoth, figuring out the genome is a relatively easy task. It's fairly easy to read the genes, but which genes go on which chromosomes? How do you then turn that huge library of letters into a set number of chromosomes, when you have no idea what that number is? And what about mitochondria? Those organelles are not built by instructions contained in the nucleus, but are transferred from mother to offspring (in rare cases, the fathers contribute some too). Nicholls does a wonderful job of laying out the problems and suggesting solutions based on research techniques that are currently being used for other (but similar) purposes.
So if you want to know what would be involved in building a mammoth, or you are just interested in learning about some cutting-edge research in cellular biology, check out this article.