Agile vs. Formal Methods
Roy Osherove blogs about a TechEd panel which addressed the subject of Agile vs. Formal methods. The blog doesn't provide a definitive answer to this question, that's because there isn't one, but it does start to explore some very important issues which your organization should consider.
A complementary article is my own Choose the Right Software Method for the Job where I compare and contrast a variety of processes such as RUP, XP, AUP, and even frameworks such as ISO 12207.