Some musical things, now.
Dearon = Bill Bailey. Singing all his songs using a synthesiser!
Maglor = Vivian Stanchel (Of Bonzo Dog Doo Dah Band fame), I just find the whole idea amusing. "Mr Slater's Silmarill" perhaps?
Moving on...
Thingol = Dylan Moran (Of Black Books fame). A drunken, angry Irish man would suite this role perfectly, I think.
Feanor = Jonathan Ross. Well, no one would take him seriously when making his speeches.
Tuin = Graham Chapman as Brian from The Life of Brian. I just think it would fit, all these bad things happening to one guy.