I met some great runners in the great state to my near north (My home state Michigan) during my lead up to Boston and they recently directed me to these Jay Johnson Core and Strengthening workouts. I am on week 3 of incorporating these into my hard days (Tempo and Track) and going to start doing a minimum of the 20 second pedestals on my easy days too. And I think they are making a difference. It seems counter-intuitive to do a semi-hard cool down after a hard workout, but I actually think it is promoting recovery while strengthening some of my weaknesses in my core and hips!
Check them out and see if you can find time to squeeze them in!