While I don't advocate the de-extinction of mammals or any mobile/motile organisms for that matter, I would love to see some plant species come back to life. And like the applications aforementioned, we can possibly save certain plants from extinction as well. I view this as a more stable option than bringing back an extinct animal.
But if we do clone an extinct species, I think it's more proper to sate our curiosity on that single specimen and study it rather than try to bring back its whole species.
Hm, I wonder if DNA particle bombardment on a single cell embryo of the extinct species can be a solution to that problem by introducing genetic diversity not limited to the gene pool of that species, which can increase the total genetic variability of the species temporarily as it recovers to an ideal population size. That sounds expensive and unreliable with current technology, however.