I like 'The Inner Game of Tennis'
not technique stuff at all, but useful.
I taught myself to play with 'Lawn Tennis the Australian Way' as a child, but I don't think it is relevant anymore.
5.0 all courter. 2 x Donnay X-Dual Platinum 99s 2 x Donnay Formula 100s (no, really!)
"Tennis isn't easy" - Corners