Here's a few more single keystroke shortcuts....
When painting (or using any tool that has opacity) press 1-9 for 10-90%, 0 for 100% to change the opacity of the tool
If a layer is active and the Move tool (or any non-painting tool) is active use the same keys: 1-9 for 10-90%, 0 for 100% to change the opacity of the layer
Press F to toggle between the 3 screen modes (Standard, Full screen w menu bar, Full screen)
Press TAB to hide all floating palettes