Im glad you enjoyed Cobalt and Melodys story. Its one of my favourites to reread too.

Have you read Games of Command by Linnea Sinclair. Kel-Patten is kind of like a half machine, half man and everyones wary of him too, but hes crazy about the heroine, whose quite amazing as well. Its SF romance.

You could also try the Black Jewels trilogy by Anne Bishop. Its dark fantasy, but the hero Damon aka the Sadist and Janelle are an unforgettable pair.

Oh, and have you read North Wolf by MA Evereaux, a bit steamy, but fits this thread perfectly.

Maybe
- Crossfire series by Sylvia Day
- Fever series by Karen Marie Moning (Paranormal romance)

And of course El James Fifty shades of Grey

And try "Beautiful Disaster" by NOT ALLOWED
Love the book...

With Lolitadr and Cj77 said, I'm just going to re-recommend the Fever series. Seriously one of THE best series I have ever read.
A bit dark though, okay a lot of dark, but you will not regret it at all. Jericho is DEFINITELY an alpha bad boy... he's about as bad as you can get.