This one is easy.
By FAR the best I've ever seen/used - and I've had physiology and pathophysiology coursework at 2 different colleges that used this text.
Human Physiology - by Vander, Sherman, Luciano.
Here is a link to a description:
And here are a bunch for sale via Amazon
: (No, I don't have any affiliation with Amazon!)
Physiology isn't an easy subject to really get a handle on, so it isn't exactly "light reading" - but I did feel that it explained everything very well if you took the time to read carefully.
Hope this helps!
p.s. I even bought the 8th edition for myself just for reference, and continue to use it regularly when I remember that I forgot something, or someone asks me a question that I can't answer!