Sprint 40 yards, walk back...Repeat
This was bread and butter during my football days, and I still love the punishment. I can do this for about 12-15 minutes before I feel like throwning up.
Otherwise, you can run at a fast pace for 30 seconds, then walk for 1:30...Repeat for about 15 minutes. It is not as painful, but still very effective.
Then it is best to do 20-30 minutes of low-mod intensity cardio to burn the released fat stores from your HIIT training.