I group shortcuts into 2 main categories:
Keyboard shortcuts - Please note that not every one of the shortcuts works the same in all programs.
Non-Program Shortcuts (use on files, desktop, explorer windows, etc.)
Switch Windows = Alt + Tab
Create Copy = Ctrl + Drag
Create Shortcut = Press-and-hold Ctrl + Shift then Drag icon
Open Start Menu = Ctrl + Esc
Instant Delete (don't send to Recycle Bin) = Shift + Delete
Refresh current window = F5
Dialog Box/Message Box Shortcuts
Move to next control (button, textbox, checkbox, etc.) = Tab
Cancel Form = Esc
Click selected button = Space
Check selected checkbox = Space
Use selected option (radio-button; "eye" buttons) = Space
General Usage
Copy = Ctrl + C
Paste = Ctrl + V
Cut = Ctrl + X
Print = Ctrl + P
Save = Ctrl + S
Save As = Ctrl + Shift + S
Left-Align Text = Ctrl + L
Center-Align Text = Ctrl + E
Right-Align Text = Ctrl + R
Undo = Ctrl + Z
Redo = Ctrl + Y or Ctrl + Shift + Z
New Document = Ctrl + N
Drag-Copy = Ctrl + Drag
Help = F1
Close Program = Alt + F4
Format Bold = Ctrl + B
Format Italic = Ctrl + I
Format Underline = Ctrl + U
Select All = Ctrl + A
Delete = Delete
Photo/Graphic Editors (Adobe Photoshop, PaintShop Pro, Paint.NET, etc.)
Adjust Hue, Saturation, & Brightness = Ctrl + U
Unselect = Ctrl + D
Navigational shortcuts