There are so many books on PS, and many are so specialised, that it's almost impossible to make recommendations; you really have to know what you want to know, IYSWIM.

For online learning I don't think you can do better than lynda.com, which has a huge resource of video tutorials on PS (and a lot of other softs as well). For $25 a month, you can watch as many as you like; it's a great deal, IMHO. Some are free to non-subscribers so that you can try before you sign up.

Steve