I have to admit, the best and most accurate bpm measurement tool is a little plugin from a programmer in Denmark. .. the plugin is designed to work with Cool Edit Pro which has now morphed into Adobe Audition.
I've used it for years .. and best of all it gives you a bpm reading down to the thousandth bpm (ie: 128.547). It can be super fast with results .. depending on how much of the wav file you hilight for the bpm calculation (very quick at testing the top and end of a song to make sure it doesn't change speed somewhere in between.) I had to do some adjusting with mp3tag to be able to store the complete info). Here is what it looks like:
Because of changes in Audition's architecture you can't use the plugin with Audition 2.0. I've found for the best bpm results, you should use Cool Edit 2.0 or Audition 1.0 (the plugin will automatically install in those programs, plus in CEP2 you can have it check the BPM while you're playing the file with the program.) I have Cool Edit Pro 2, Audition 1, Audition 1.5 and Audition 2 installed on my computer right now .. overkill? no, I just use each one for it's strengths or multi multi multi multi tasking sometimes.
Here are some links:
www.pyramidedata.dk - BPM Plugin info
Direct download link for version 1.01 of the plugin
(note that it's "pyramide" data if you need to type in the link manually for some rteason. Also,
he has some other user-friendly bpm tools on his site, as well.)
I poked around for the old Cool Edit Pro 2.0 for you, but didn't find anything to download (I'm sure with further searching you can find it out there). Let me know if you need any help with any part of this.
P.S. It doesn't put the bpm data into the file ... however, if you're editing or using music for dj work or re-editing, you're hopefully going to be using wav files for this process (if you want accuracy and assured clarity of sound) and there is no tag fields in a wav file for bpm info. My solution was to put the bpm at the front of the filename, that way things were sorted by bpm etc. The file names looked something like this:
<b>131.168 Whitney Houston - Learned From The Best (Some Version).wav</b>
The best program for clean speed/pitch adjustments is Sound Forge (used to be Sonic Foundry, now Sony).