Here is the list of gmail shortcuts.
Formatting
<Ctrl> + <Shift> + 5 : Previous font
<Ctrl> + <Shift> + 6 : Next font
<Ctrl> + <Shift> + - : Decrease text size
<Ctrl> + <Shift> + + : Increase text size
<Ctrl> + b : Bold
<Ctrl> + i : Italics
<Ctrl> + u : Underline
<Ctrl> + <Shift> + 7 : Numbered list
<Ctrl> + <Shift> + 8 : Bulleted list
<Ctrl> + <Shift> + 9 : Quote
<Ctrl> + [ : Indent less
<Ctrl> + ] : Indent more
<Ctrl> + <Shift> + l : Align left
<Ctrl> + <Shift> + e : Align center
<Ctrl> + <Shift> + r : Align right
<Ctrl> + <Shift> + , : Set right-to-left
<Ctrl> + <Shift> + . : Set left-to-right
<Ctrl> + \ : Remove formatting
Compose and Chat
<Shift> + <Esc> : Focus main window
<Esc> : Focus latest chat or compose
<Ctrl> + . : Advance to next chat or compose
<Ctrl> + , : Advance to previous chat or compose
<Ctrl> + <Enter> : Send
<Ctrl> + <Shift> + c : Add cc recipients
<Ctrl> + <Shift> + b : Add bcc recipients
<Ctrl> + <Shift> + f : Access custom from
<Ctrl> + k : Insert a link
<Ctrl> + ; : Go to previous misspelled word
<Ctrl> + ' : Go to next misspelled word
<Ctrl> + m : Open spelling suggestions