Switch it up always...
with a dumbell Do some axe chops and squats and rear rows targeting your core and pretty much everything else...I love the kettlebell but hard to get a hold of those.
I workout regularly and when I plateaued I did this and my abs started getting defined after only two iterations of this! I like freeweights on everything personally, except triceps and chest with the lat pulldown rope and the d-rings for chest. Don't just do pushups do offset pushups, medicine ball pushups,etc.,etc.,etc. you get it you get it
Oh and I did that INSANITY workout and as far as Cardio and strength endurance goes, IT KILLS...buy now for only 5 easy payments of 39.99!!j/k I downloaded it