I can't believe that I pick this, of all threads, as my first Tri Forum post here on ST, but here goes......
I did my first round of P90X in '05 and it's what got me into racing and triathlon - I loved the competition aspect of it (if you do the program correctly, you are competing with yourself each and every workout - weight lifted, reps, etc.) and wanted more with my improved fitness. I still use the program and other Beachbody programs as they fit into my SBR training plan, and think they are truly fabulous for folks who are interested in this sort of training as an augmentation to SBR.
Two years ago I joined the Beachbody team as a "coach" (hate that term for this job but it's what they use) - I'm a reseller of the products in addition to helping people with choosing the right program, structuring a training plan around SBR, exercise modifications, and motivation/accountability (all of those extra bits are free). TRI mentioned P90X+ and Insanity - two more VERY good programs that could easily fit into a triathletes schedule nicely. ShaunT (creator of Insanity) is coming out with a follow-up called Asylum due to be released in early '11 that has more of a sports specific aspect to it (ladder drills, suicides - the clips remind me of some drills I used to do as a high school basketball player, and some drills my son does in football).
If anyone is interested in hearing more about any of the Beachbody programs, seeing clips of the workouts, etc., feel free to contact me and I can hook you up. For the people here already doing the X or Insanity, I'd love it if you'd consider signing up under me as your coach (all free - I'll just keep you apprised of up and coming releases and can help with any questions or issues you might have). My email is: mspina@beachbodycoach.com, or check out my site (where you can find the product list and info on how to sign up with me):
http://www.beachbodycoach.com/mspina