[Tiwaz]

In the console type: bind key "say *nn"

key is the key you want to bind to the taunt, * represents the 'v', n is a number.

Example: bind m "say *31"

Binds the v 3 1 taunt (Yes Sir!) to the m key...

If you only want to bind some keys, otherwise use the complete list (Bazooka_Joe's link).

If you want to bind numpad/arrows/symbol/command keys to taunts, use capitals:

UPARROW, DOWNARROW (normal arrow)
KP_UPARROW, KP_DOWNARROW (arrow on keypad)
BACKSPACE
KP_MINUS
KP_PGUP (keypad PgUp (the 9))
PGUP (normal Page Up)
KP_STAR
HOME
KP_ENTER

etc.