As probably most of us know, the SR-71 Blackbird holds the altitude record for leveled flight for (manned) jet planes (and ground-launched planes) at 90,000 ft MSL. However, the very altitude record in leveled flight is probably held by a rocketplane, such as the Bell X-1 or the North American X-15. Is there an altitude record for leveled flight that surpassed that of the Blackbird? What's the record for the highest horizontal flight by a rocket (or any other type of) plane? May include unmanned ones.
Edit: To make it clear, my question asks for the altitude record of a winged aircraft that could sustain this altitude aerodynamically. But Abdullah answered my question anyway, it was the NASA Helios propeller craft (which looks a bit weird but still is a winged aircraft) that reached and sustained an altitude of 96900 ft (29,500 m). Wikipedia says this is the altitude record for aerodynamic horizontal flight.