Rainbow 6: Raven Shield to Vegas, (or any other shooter where you use Q and E to lean).
In Vegas you use Q to throw grenades, which is quite convenient actually, but I used to throw grenades at a wall when trying to lean for awhile, which kinda sucks.
And other games where I mess around with mouse buttons and Alt, F or G, trying to fit in the best combination of Grenade/Use/Command team/Open/Stealth/Melee/NV.
Most cover based shooters I like to use Space to get down and stick to the wall, of course this can sometimes lead me to jump OVER the cover right into enemy fire on some games.