i haven't had sex, but i've.. well, i've basically had sex. let's not get into it. ;P
anyway, my vote is the one of anticipation. also, i really enjoy the rapid breathing, the first touches... i wish first kisses were an option. it's insane to feel the amount of passion and lust in the kiss that leads to it all.
by the way, would you mind answering my question, if you could? it's on my profile. i need some advice, and you seem rather experienced. i'd appreciate it.