Terry O’Quinn is mine. Decades of great performances in bit roles and B movies. He finally had a big-visibility role on Lost, but with the departure of that show he risks slipping away to just being “that one guy from Lost”.
He could easily carry a premier series as the lead.
The original Jennifer, Claudia Wells. So much yummier than Elisabeth Shue.
Took 22 years off from Hollywood, but seems to be coming back.
And was the original Meg Griffin.
She’s the Golden Globe nominated star of the #1 cable series of 2010 among 18-49 year olds. So she isn’t doing THAT horribly.
From the 1950s Ralph Meeker. Looked like he had a breakthrough in “Kiss Me Deadly” and was in Kubrick’s “Paths of Glory”. But never progressed. Every now and then I see him in an old tv show like “Route 66” and wonder what went wrong.
Oded Fehr, from The Mummy franchise. I thought " Wow" and poof, where’d he go?
Jason Bateman, although that could be changing soon.
I knew him from UC: Undercover. He’s alright. Handsome man, certainly.
Does some TV work, seems to be doing voice acting now.
Well, he’s just been added to the cast of the new Hawaii 5-0 so he seems to be doing well.
One actor I’ve liked for a long time but until recently with Suits never seemed to get a lot of publicity was Gabriel Macht.
Also I don’t know his name but I thought whoever played Jake Ryan in 16 Candles would be huge considering how all the girls in my middle school reacted to him, but he just disappeared.
I also wa surprised that Ed Marinaro never got huge or Betty Thomas(huge Hill Street Blues fan here).
Me, too. She became quite the successful Director - quite a few hits like Private Parts and Dr. Doolittle remake, and maybe some misses, too 
His name is Michael Schoeffling. I only know this because around six years ago, a girl told me I looked like him. I had never seen 16 Candles, but I looked him up. He also played “Kuch” in the great Vision Quest with Matthew Modine, one of my favorite movies. Trivia - the screenplay was written by Darryl Ponicsan, who also wrote The Last Detail, another one of my favorite movies.
A couple of other names occurred to me.
Heather Thomas from the Fall Guy. She was gorgeous, incredibly charismatic and just disappeared.
Dale Midkiff, the star of this really terrible scifi show from the 90s called Time Traxx.
Finally, Chiwetel Ejiofor. The operative from Serenity.
I thought he was fantastic and would be huge but he just disappeared as well.
I’ve seen him in six movies since then, most notably Inside Man, Children Of Men, American Gangster, and 2012.
There’s a few from Deadwood that I thought would blow up - the woman that played Calamity Jane and the woman that played Alma Garrett, most notably.
You don’t even want to dignify Salt with a name?
Saw a commercial the other night that he’s going to be on Hawaii 5-0 as one of the main characters. Working with one of his former Lost co-stars, as a matter of fact.
Didn’t see it.
I always though David Faustino who play Bud on Married w/Children was a terrific comic actor with great timing. I think he played well off Christina Applegate. He did the physical comedy very well.
I brought him up in the similar thread re leading men. I couldn’t take my eyes off him.
He was one of the stars of the Showtime series Sleeper Cell where he played Faris Al-Fariq, just about the most chilling and believable portraits of a Jihadi I’ve ever seen. He also played a Mossad agent on V and has a recurring role as one on Covert Affairs.
More than a few fans of the show, including myself, would like the idea of him being a series regular because he has vastly more chemistry with Piper Perabo then Ben Mercer, the guy we’re supposed to believe she’s in love with.
One I’ve mentioned in threads like this before: Bruce McGill. I remember seeing him in Animal House and thinking he was going to go on to be a major star. But while he’s worked steadily through the last thirty years, he’s never risen above being a supporting actor.