Harrington on Hold'em definitely the best.
i'm reading it and it hasn't helped me much yet (cuz i ended up playing more ringgames lately) but i know it's gonna help me out
i also think Supersystem 2 was interesting, i never read supersystem 1 so i'm not sure...
Sklansky's Hold'em for Advanced players is not so bad, but it's hard to read so much that it gets boring reading so much:S
i heard there was a new book by barry greensteign coming out. hope it's intersting. i'm gonna buy it so