To change it up a bit here's my extreme cardio routine. I don't have a heart-rate monitor (yet, fingers crossed) but I created four levels of exertion to guide myself through it with the paces based on talking, figures ;) : Level 1, conversation; Level 2, short sentence; Level 3, one word answers; Level 4, short of breath (intense sprint).
0:00-5:00 Warm up in Level 1
5:00-7:00 Moderately increase to the peak of Level 2
7:00-9:00 Continue to increase (level/minute) until the top of Level 4
9:00-11:00 Return to Level 1 for recovery
11:00-33:00 Repeat the steps above twice
33:00-40:00 Cool down in Level 1
I'm no expert whatsoever and I am definitely new to running but I looked through quite a number of fitness magazines, books, and websites to develop this workout. I love how the constant change of speed keeps my body interested and the high intensity clears my head. Plus, if nothing else, I am surely going to be s-o-r-e tomorrow :).