I'd never heard about Cap being modelled on Fred Mac Murray, and I'll be goshdurned if it didn't hit me like a ton of bricks. No doubt about it, they're dead ringers.
I'd give my eyeteeth to know who Prince Namor, the Sub-Mariner is based on! Ditto for the equally weird looking Curt Swan version of Lex Luthor.
Though I have heard that Gil Kane based the appearance of Hal Jordan on Paul Newman. This makes sense; of all the Silver Age heroes, Green Lantern seemed the best-looking. He wasn't a muscled lumberjack type like Superman or Batman; he was more kind of Greek. Nobody ever drew GL the way Gil Kane did, for sure.
Sting was the inspiration for John Constantine, though that should be especially obvious.
I can't confirm this, but I heard somewhere that Cosmic Boy's appearance was originally based on the pop star, Fabian.
Tinkerbell, too, was based on Marylin Monroe's measurements. And there was a rumor that Dr. Evil from AUSTEN POWERS, at least in personality was a parody of Lorne Michaels.