I stumbled on this from a running blog I visit frequently. I thought what a great idea to get you challenging yourself on your own. So here it is, and now I am challenging you! If you are thinking "ho hum Savich" this is too easy, lower your knees to a hover just above the ground and raise them again. Still thinking this plank is too easy, check out the image below the calendar- you can try this position which will work your triceps and shoulders as well.
Not sure why the plank is beneficial to you at all? Livestrong.com has this great post of the Benefits of a Plank!