Nothing official (obviously), but I've had some ideas kicking around for a few years and thought I'd share them. Would love to hear other people's ideas, as well.

Homestar: Jon Arbuckle (Garfield)

Strongbad: Green Ranger (Mighty Morphin Power Rangers)

Pompom: Katamari (Katamari Damacy)

Marzipan: Lady Miss Kier (singer of Deee-Lite)

Strong Sad: Linkara (Atop the Fourth Wall)

Strong Mad: Machamp (Pokémon), Roger Freeland (bassist, HALYX)

Coach Z: Eminem as Max Headroom (Rap God music video), Boyfriend (Friday Night Funkin)

Bubs: Dante Hicks (CLERKS)

King of Town: King Harkinian (Zelda: Wand of Gamelon/Link: Faces of Evil)

Poopsmith: Turboman (Jingle All the Way)