Chipping in here with the three textbooks which (of those which are readily available) I've found the most helpful to date:
Flying qualities and flight testing of the aeroplane, by Darrol Stinton.
Flight testing homebuilt aircraft, by Vaughan Askue
FAA AC23-8, flight test manual for normal, utillity and aerobatic category airplanes.
Regarding the SETP handbook mentioned in NES' original post - it's useful and I certainly have a copy on the shelf but to be honest it falls more into the category of "hints for advanced players" rather than being useful when coming into flight test. I'd suggest starting with the first two I've mentioned here, and some of the excellent historical and biographical books other people have mentioned (to which I'd add Roland Beaumont's "Fighter Test Pilot" and "Aerospace Flight Test Engineer" by William Murry Thompson).
G