1. Ava Gardner in KNOTS LANDING
I found her the most entertaining celebrity stunt cast, and because Knots Landing wasn't an out-and-out glamour show it felt extra special to watch her in that particular soap environment. Well of course Greg and Claudia's mother couldn't be
just anyone.
2. Helmut Berger in DYNASTY

I just
can't think of a better choice for Dynasty's EuroPeewee than the Dorian Gray of seventies Euro Cinema. His previous work made him the perfect shambles for the toned-down Carringtons but, alas, it wasn't meant to be for American television anno 1984.
3. Lana Turner in FALCON CREST

Jacqueline Perrault is one of SoapLand's most fascinating characters, but that has more to do with what she represents rather than what she did on screen.
I've never seen a Lana Turner movie so I don't know if there's some kind of parallel going on here (probably not).
Either way, it's a very big name in the TV soap genre, but having her play opposite
other Hollywood veterans Jane Wyman and Mel Ferrer makes it feel a wee less special than Ava on Knots (with the benefit of hindsight of course).
4. Christopher Atkins in DALLAS
Obviously he was cast for his semi-scandalous Blue Lagoon fame, and I think it was an excellent choice.
5. Jane Russell in THE YELLOW ROSE

I was going to say that this situation was similar to my #1 choice, but I think The Yellow Rose lent itself to big name casting more than Knots Landing did.
But they didn't, therefore Jane Russell's guest role appears to be super stunt-y - but it also makes sense that they asked
her, and not another Hollywood icon (well, they couldn't ask Joan Crawford).