Apollo 11 landing sequence
This one may sound like an easy choice but, having read so much about the Apollo program and understanding the level of complexity of the events leading to a moon landing, this video makes me sit at the edge of my seat every time. Especially with the added stress of the 1201-02 alarm that almost forced them to abort the landing. (info about the 1201 alarm)
Space Shuttle SRB Flight
This is a long one to watch but it's worth it. The camera is attached to the top of one of the Space Shuttle Solid Rocket Boosters (SRB). The strange feeling of seeing the ground 'fall' away at this ridiculous speed is hard to beat. After the noisy first part of the takeoff, there is a change in the sound while the rocket leaves the dense atmosphere followed by the silence after the separation. But the most awesome part is when the booster enters back into the dense air with the eerie moaning-sound of the empty cylinder growing into a full roar while the rocket is slowing down to terminal velocity.
SpaceX Grasshopper test
This video just climbed into my top three list for the simple reason that it is filmed from the air. This was done probably by using a sort of radio controlled camera platform (e.g. Quad-copter). It is a strange feeling, to virtually be there and float next to this monster while it just stands in mid-air. You expect a rocket to either do nothing on the pad or go full throttle but to see this delicate precision, now that is crazy cool. SpaceX made it look like they do this every day... but wait.. they ARE doing this every day. Go SpaceX!