depends on your experience, and what you are playing
but heres one for every situation
to get better, at tour and your a long ball player, harrington vol1-3
no matter long or small baller (tour) kill everyone, is a must
if your playing sit and gos, get sit n go strategy by collin moshman
playing live and need reads, get read em reap by Joe navaro
for bet sizing i like phil gordons book(a lot of details)
need help with
odds-matthew higglers odds and probability
for pshchology try alan schonmaker book
if pokers or bad beats getting to you get zen and the art of poker
i like gus new book, just to read how he thinks(i do not think like him)
also harrington has some good cash game vol.s
thats all i can think of right now, if i think of more ill add later. gl