Harry? Lee Pace or Joe Flanigan for looks, no question... though Nathan Fillion's personality is PERFECT, lol. 

I can't NOT think of Krista Allen whenever Lara Wraith is on the page...yowza... and someone else mentioned Brad Pitt for Thomas...but of course! Though Matt Bomer would work too.

Neal McDonough is stuck in my head as Morgan, even though he doesn't quite match the description...sometimes my brain refuses to agree with what's on the page, haha.

Karrin - I have a sort of miniature Jennifer Esposito with blue eyes in my head when I picture Murphy. 

Eva Mendes was my Susan...

and Sigourney Weaver (a'la Ghostbusters, all possessed) is my Leaninsidhe!

Joe Mangianello would be a great Michael. sigh.

Amber Tamblyn with blond hair is how I imagine Molly (again, I KNOW, not really a fit, based on the description, but the heart wants what it wants, lol)