The author who always comes to mind when I think of sexual tension (an essential ingredient to good H/h chemistry) is Linda Howard. I remember specifically reading Dream Man by her and there's this scene when the couple, who have actually already been intimate, go on a drive. They're in the south, and as he's driving, one of those sultry, southern rainstorms is rolling in. The air heavy with the impending rain, the heroine decides it must be time to tease the hero. She begins touching and gets him practically frothing at the mouth. He breaks land/speed records getting her home and into bed. I remember practically fanning myself as I read the book. What I like about Howard's style is that when she wants to, she can build that tension to a fever pitch, to where I'm screaming in my head, "JUST DO IT ALREADY!"
Another couple who I thought had terrific chemistry are Lillian Bowman and Marcus Westcliff from Lisa Kleypas' It Happened One Autumn. The reader knows almost from their first encounter that the two of them are destined for each other. Mostly because she's a hoyden and he's a man of stature and dignity. You just know that she's going to live to muss up his hair. My favorite scene between them is when he finally kisses her. They're in a spot where they could easily be caught. But they both are swept away by the moment, and sort of sink into the kiss. They pull apart completely rattled and wondering what the heck got into them. It's this marvelous scene and one that made me yearn for them to consummate the relationship.
Or how about Lucas and Sascha from Nalini Singh's Slave to Sensation? Remember when Sascha, a Psy who has had emotion programmed out of her, begins dreaming about Lucas? She doesn't realize that they are mentally connected and he is experiencing her extremely erotic dream right along with her. And she's trying to make everything go the exact way she wants it to, but he's pushing her boundaries, even then, in her dreams, making her go farther than she thought she could. It's heady stuff and definitely what made me fall for Lucas as a favorite hero.
So tell me, which characters do you think have the best chemistry? Who are some of the authors who write terrific sexual tension or chemistry? What are your favorite books with incendiary reactions between the Hero and Heroine?