I remembered one more – though her acting credits are not the focus of her career, Alanis Morrisette started out on the Canadian/Nickelodeon program You Can’t Do That on Television.
And seriously folks, if you want to protect your posts, lock your doors when you sleep. I keep odd hours and I’m a tiny woman who can fit through 99% of household windows.
Yet another nitpick: Laurence (then billed as Larry) Fishburne’s role was Cowboy Curtis.
Also, I thought “Alanis!” about halfway through reading this thread, only to see TeaElle had mentioned Ms. Morissette. Hey, there’s another nitpick, although I admit I had to check the trusty old IMDb to make sure I had the spelling correct… 
He didn’t host the show. He was just one of several featured actors. The show didn’t really have a host.
BTW, Easy Reader was my idol when I was a kid.
Leonardo DiCaprio was on the new Romper Room.
Rita Moreno was also on The Electric Company and Christina Aguilera was a Mousketeer around the same time as Britney & Justin.
D’oh! Thanks! Wasn’t there a “Carl” on the show? Maybe Hartman was Captain Carl? Or I’m just imagining things.
If my Lynne Thigpen nomination isn’t kosher because of her prior credits, I’m going to challenge Rita Moreno on the same grounds.
Cool with me. I thought about that after I posted.
Steve Burns from Blue’s Clues, though he hasn’t done much non-Blue related acting yet.
Burns has turned to a recording career, though he did have a memorable guest role in Homicide: Life on the Streets
Chuck McCann started out as a kid’s show host in NYC and went on to a long career as a bit actor and voice actor in cartoons like Powerpuff Girls and Duck Tales.
Does Soupy Sales count? His kid’s show was his first national exposure but he hosted a Cincinnati dance show aimed at teenagers before that.