'Strengths Finder 2.0' from Gallup by Tom Rath
Of all of the skills assessments out there (and I have tried a LOT of them), this one I found to be the most insightful. The book itself details the 34 categories of innate talents. When you take the online assessment, you receive two reports: (1) Strengths Insight Report; and (2) Your Signature Themes. In combination these reports identify your top five talents, describe how those talents make you stand out, and detail how you can utilize your talents to more effectively move forward. My favorite part of the assessment was the "Ideas for Action," where, based on your top five talents, Gallup generates a list of "to do" items that tell you exactly how to put your skills to best use.