This sound editing company, Twenty-First Century Entertainment (formerly known as 21st Century Sound Design Corp.) was founded by Joel Valentine, who developed "The Producer's Sound Library ", and was mentor to Spongebob sound designer Jeff Hutchins. They worked on the following shows, movies and TV specials, mainly ones from Hanna-Barbera and Cartoon Network. They usually credit sound editing only.
- 2 Stupid Dogs/Super Secret Secret Squirrel (2 Stupid Dogs segments only)
- The Halloween Tree (1993) ?
- The Town Santa Forgot (1993)
- What a Cartoon (many episodes) - Audio Services, Sound Editing
- Jonny Quest Versus the Cyber Insects (1995) - Sound Effects Editorial
- Dexter's Laboratory (first two seasons only)
- Johnny Bravo (first 3 episodes only, rooted from What A Cartoon!) - Audio Services
- The Powerpuff Girls (Seasons 1-6 only, plus the movie and "The Powerpuff Girls Rule!")
- Samurai Jack (Seasons 1-4; Joel does work on Season 5 though)
- Codename: Kids Next Door (2001 pilot "No P in the O.O.L." only)
- My Freaky Family: Welcome to My World (2001)
- The Powerpuff Girls Movie (2002) - Sound Editorial and Design
- Dexter's Laboratory: Chicken Scratch (2002) - Sound Effects Editorial
- Foster's Home for Imaginary Friends
- Welcome to Wackamo (2006) (uncredited; Joel was a sound editor on this project)
- Chowder (TV Series) (2007 pilot only, uncredited; Joel was a sound effects editor)
- The Powerpuff Girls Rule! (2008)
- Korgoth of Barbaria (2006)
- Sym-Bionic Titan