Dinosaurs are out of the question now, but Stewart Brand pushes to revive more recent extinctions:
Close examination of the genomes of extinct species can tell us much about what made them vulnerable in the first place. Were they in a bottleneck with too little genetic variability? How were they different from close relatives that survived? Living specimens will reveal even more.
Stuart Pimm disagrees:
In every case, without an answer to “where do we put them?”—and to the further question, “what changed in their original habitat that may have contributed to their extinction in the first place?”—efforts to bring back species are a colossal waste.
The Dish 