Scheirer, Eric D. "Tempo and beat analysis of acoustic musical signals".The Journal of the Acoustical Society of America, Vol. 103, No. 1. (1998), pp. 588-601.
Another good article is "Tempo and Beat Estimation of Music Signals" by Alonso, David, and Richard.
 Beat This. A Beat Synchronization Project. http://www.owlnet.rice.edu/~elec301/Projects01/beat_sync/beatalgo.html (8 Nov 2009)
Matlab .m files of their algorithms are available for download.
Digidesign. Drum Hit and Sound Replacement AudioSuite Plug-in. http://www.digidesign.com/index.cfm?navid=115&itemid=1059 (8 Nov 2009)
Audacity 1.3.9 features a beat finder tool for beat analysis which has good graphical output shown below the waveform view.
Trillium Lane Labs features a Plug-In called "Drum Rehab".
Mark of the Unicorn features a "Beat Detection Engine" in Digital Performer which is useful for beat stretching.