[epic]

Here are the ones I use the most:

[ and ] to adjust brush sizes i dont think i could live without that one.
Alt + backspace fills the layer or selection with what ever color you're using.
The mouse scroll wheel to zoom in and out (mouse down zooms in mouse up zooms out) this only works if you dont have a scroll bar on the image though.
I also use this shortcut alot but its a combination mouse/keyboard shortcut: click the create new layer button to create a new layer at the top of your layers list (if it isnt at the top move it) then holding the Alt key click the layer tab and drag down to merge visible list. This merges the visible list into the new layer at the top and keeps all your layers below it. (alt + Ctrl + Shift + E) works to but i think its easier the other way.
I use alot of the above mentioned ones too.