Monotonous Sex

Ok, I'm not implying that my sex life is at all monotonous, but my husband and I encountered something today which made us realize we do have certain expectations of sex. You know, habits that have been formed and things we have come to expect out of patterns our sex life has developed. My husband was getting ready for work and I decided I'd surprise him with one of his favorite sexual favors. As I was unzipping his pants he said, "We don't have time to have sex." I was confused because I was just planning on pleasuring him a little bit before he had to go off to work, so I zipped his pants back up. I then asked him if he had a problem with what I was going to do, and he said that he knew where it would lead and we just didn't have time to have sex. This may not seem like a big deal, but it revealed to us that we have made it a habit to pleasure each other then follow that with sex, rather than just pleasuring each other for the fun of it. When I was faced with this reality I felt sad that we had let our sex life turn even a little bit monotonous and predictable. I should be able to surprise my husband with a blow job and not have him feel obligated to have sex too. 
So what do we do to take that predictability back out of our sex? I've been trying to be more spontaneous lately just to keep the spark alive and make sure he's satisfied, but obviously I've been doing somewhat of the same things over and over again. I'm going to make a bigger effort to totally switch things around and make sure he can't get bored and I hope it works. We have an awesome sex life aside from apparently being a little predictable (I'd say at least 2 orgasms a session is pretty satisfying) but I'm hoping we will overcome this quickly and bounce back into a non-routine sex life where neither one of us knows what's coming next (no pun intended).
Anybody else experience some sort of monotony in their sex life? What did you do to combat it? I'd love to hear different ways to kick monotony, predictability and repetitiveness out of the bedroom!