I tried Mixmeister and Tangerine. Mixmeister worked okay but you can only analyze one song at a time and import the info back to iTunes one song at a time. Because I have 1500 songs in the library, I decided to purchase Tangerine. It turned out to be the best $25 I had ever spent. It takes seconds to analyze my whole library and about 10 min to export the info back to iTune.
For most songs (I tested 10), Mixmeister and Tangerine gave the same BPM results. They counted one song very differently. Tangerine does not appear to be as accurate as Mixmeister after I manually counted a small sample of songs where the 2 softwares count differently.