Every tool in Photoshop has a single letter you press to choose that tool. I must be honest and say that I don't remember or use every one, but here are some of the ones that my fingers press, seemingly without any help from me some times:
(the keystroke is capitalized and bold)
and I for eyedropper (at least that one sounds the same)
I also press
Q to get in and out of Quick Mask mode
D to set my colors to default
X to swap my foreground and background colors
Gee, there's more than I thought, so maybe I'll think about it some more and add more tomorrow....