Hmmm...interesting twist on this! Here are the one's that come to mind off the top of my head. I'll have to think some more about others. (Not sure if you would consider most of these B actors, but they're certainly not Academy Award winners either
):
Cosmic Boy ~ David Lasher
Lightning Lad ~ Andrew Shue
Saturn Girl ~ Sarah Michelle Gellar (Buffy)
Princess Projectra ~ Jennie Garth (90210)
Triplicate Girl ~ (oldest daughter from Eight Is Enough)
Phantom Girl ~ Alyssa Milano (Charmed)
Invisible Kid ~ Matt Lawrence
Mon-El ~ James Marsden (X-Men)
Brainiac 5 ~ "Doogie Howser"
Sunboy ~ Mark-Paul Gossalear (sp) (Saved By The Bell)
Element Lad ~ Christopher Atkins (Blue Lagoon)
Dream Girl ~ Heather Locklear
Ultra Boy ~ Joey Lawrence (Blossom)
Star Boy ~ Barry Watson (7th Heaven)
Colossal Boy ~ Jeremy London (Party of Five)
Timber Wolf ~ David Boreanaz (Angel)
Chemical King ~ Jason Gedrick (Iron Eagle 1)
Matter Eater Lad ~ Kirk Cameron
Shadow Lass ~ (can't think of her name, but the actress from "King of Queens")
Mysa Nal ~ Melissa Joan Hart (Sabrina The Teen Age Witch)