One that has worked greatly for me is probably the same one that you described. Jab to the face, Right Cross to the body (make sure he takes his guard down to block) and a roundhouse to the head. Jab, Cross, Roundhouse. Another combination that has worked "okay" is Jab-Cross-Cross. It's for use with a low-guard, otherwise it will miss a lot of power. Great for Kyokushin sparring. And finally, one of my favorites. More of a setup. Jab and create some distance, the put in a LONG front kick to fend off your opponent for a few seconds, then go ahead with a massive back side kick. Worked a few times. Side kicks in general are great, actually. As specially for defense. No combination needed.