alt-left click = dblclick 
shift-left click - select more then one cards 
ctrl-left click - add 1 pt of damage to a target (creature or player) 
ctrl-right click - remove 1 pt of damage to a target (creature or player) 
ctrl-shift left click - put the name of card in the chat box 

right drag and drop - draw a red arrow to show targeting 
shift-right drag and drop - draw a yellow arrow to show blocking 
shift-left drag and drop (from somewhere to play) - play a card face down (this is really useful for cards like vampiric tutor 
where 
you have to pull out a card, shuffle your library and put the card on top, all without the opponent seeing the card) 
shift-left drag and drop (from somewhere to library) - put card to bottom of library (if without shift - on top library) 

double click untap phase (in your turn) - untap all permanents and move to the next step 
double click draw phase (in your turn) - draw a card and move to the main phase 

ctrl-d - draw a card 
ctrl-r - undo last draw
ctrl-u - untap all permanents 
ctrl-s - shuffle library 
ctrl-t - create token dialog 
alt-t  - create first token from predefined list
ctrl-f - flip a coin 
ctrl-i - roll a die 
ctrl-m - take a mulligan
ctrl-d - duplicate card
ctrl-l - Set Life 
ctrl-e - take an extra turn 
ctrl-Enter - end turn 
ctrl-Space - next phase/step 
[ctrl/alt] + ['-'/'='] - change P/T
shift+Enter - set note to card(s)
f11, f12 - add/decrement life 
F2 - new game dialog 
Alt-Enter - Full Screen mode 

(next keys in solitaire mode only) 
ctrl-shift-d - draw a card to opponent 
ctrl-shift-u - untap all opponent's permanents 
ctrl-shift-s - shuffle opponent's library 
ctrl-shift-t - create token dialog for opponent