Inhaling
Argon gas will have the opposite effect of Helium, instead making your voice much deeper/
lower, due to it being heavier than air.
The only time I have seen it was watching Jay Leno, where one of his guests had Fun with Chemistry. Inhaling Argon gave him a deep, baritone voice, like Arnold Schwarzenneger, as he said "I love you, baby! I'll be back."
The Argon gas is denser, so it passed though his vocal cords and created a deeper tone. Since it's heavier than air, it doesn't fade like Helium does. Instead of floating upwards out of the lungs, it pools at the bottm due to gravity. Jay Leno had to bend way over and blow really hard a few times. Since by doing that his mouth was lower than his lungs, eventually the gas floated down out of his mouth. There are gases other than Argon that they could have used, though you'd want them to be inert so they don't harm you. Sulfur Hexafluoride was used to the same effect by Adam Savage from Mythbusters in an episode.