Diablo II:

M - View Message Log
/time - typing this in game brings up a blue battle.net calendar, showing the time and date.
Tab - View Full Screen Map, *Shows game name and password*
C - View Character Screen
I or B - View Inventory
T - View Skill Tree


World of Warcraft:

Enter - Open Chat Box
R - Open Chat Box and set it to respond to last sent private tell
Shift + C - Toggle Combat Log
C - View Character Pane
B or F12 - View Bag
P - View Spellbook
I - View Abilities
Shift + I - View Pet Book
N - View Talent Pane
Shift + P - View Pen Pane
U - View Reputation Pane
K - View Skill Pane
L - View Quest Log
Esc - Game Menu
M - World Map Menu
O - View Social Pane
V - Show Name Plates


Guild Wars:

F5 - Open Backpack
F6 - Open Belt Pouch
F7 - Open Sack 1
F8 - Open Sack 2
Enter - Open Chat Channel
I - Open Items
J - Open Attributes Screen
K - Open Skills Screen
L - Open Quest Log
M - Open Full Screen Map
N - Open Network Panel


RuneScape:

F1 - Inventory Menu
F2 - Equipment Menu
F3 - Prayer Menu
F4 - Current Spellbook or Summoning Screen
F9 - Reply to Quick Chat
F10 - Quick Chat (area specific) Options
F11 - Repeats Quick Chat Dialogue
Insert - Clan Chat Menu
Up Arrow - Camera Up + looks down
Down Arrow - Camera Down + looks horizontally
Right Arrow - Camera Right + rotates
Left Arrow - Camera Left + rotates
Esc - Close Quick Chat
Alt + F4 - Close Browser Window
Tab - Reply to Last Private Message