Stuff you haven't/wouldn't do before.
Watch a farily hardcore porn movie and list the things they do in it as either something you have or something you haven't done, then take the list of stuff you haven't done, and do it.
Porn movies are the way they are because they're a cinematic manifestation of every guys idea of fantasy sex, of course reality sex is much tamer, make your sex more like the fantasy and you can't go wrong.
Also, find out what he likes, ask him if he's got something in mind or any secret fantasies or fettishes he hasn't told you about, make him feel comfortable to express his desires, they may very well be something he wants to do, and is just afradi to ask for.