I highly recommend the http://www.GetMaccaX12.com workouts from Chris McCormack.
I've been experimenting with them the past couple weeks and they're awesome for beginner all the way up to advanced triathletes:
My blog is at http://www.BenGreenfieldFitness.com
Also, I'm giving away a free 7-part series on "How To Become Superhuman" at http://www.SuperhumanCoach.com