[Stig Eliassen]

The best method depends on several things. How tight you need the tempo map to be, how defined the rhythm/transients are in the audio you're mapping to, how variable the tempo is in the audio, etc.

Identify Beat works fine, but using it down to every beat gets tedious fast.

Beat Detective also works fine if the audio has pretty clear transients, and a relatively steady beat, and you can create Bar|Beat markers in pretty big chunks at a time.

You can also record yourself tapping, say, quarter notes on a MIDI keyboard, and then analyze the notes with Beat Detective to create a tempo map.