His other films include Better Off Dead, Big Bully, One Crazy Summer, Bad Medicine, National Lampoon's Van Wilder, Smokin' Aces, DodgeBall: A True Underdog Story, Jingle All the Way, Southland Tales, and Beer for My Horses.

He also had a recurring role as Herbert Viola on the television series Moonlighting, and he played the part of Ahmet Ertegun in the biographical film Ray (2004).

Armstrong provided the voices for Mr. Moleguaco and Mr. Bugspit on the Disney Channel original series The Emperor's New School and The Buzz on Maggie.

In the feature film Ray, for preparation for his role as music executive Ahmet Ertegun, he had the top part of his head shaved to simulate male pattern baldness.

In 2008, he guest starred on the iCarly episode "iStakeout" as a convenience store clerk who was suspected of making unauthorized copies of films.

2009 found Armstrong playing a paranoid character in a mental institution on the House season six premiere, "Broken".

In 2010, Armstrong made a guest appearance on the television show Glory Daze and began voicing the main character on the animated series Dan Vs.

In 2011, he appeared on an episode of Curb Your Enthusiasm, and has a recurring role as attorney Peter Goldman on season seven of The Closer.

The series, which pits contestants with expertise in a variety of geek interests to see who will be crowned with the eponymous title, premiered in January 2013.

Additionally, Armstrong is a fan of Washington Irving, Laurel and Hardy, and Sir Arthur Conan Doyle's Sherlock Holmes stories.