Cunnilingus and/or
fellatio. Mutual simultaneous oral sex is
sixty-nine.
Oral sex occupies the middle ground in sexual ethics. Bill Clinton famously claimed that while he had received oral sex, he was nevertheless speaking factually when he claimed not to have had sex with that woman. Ordinary citizens, especially those for whom virginity is important, can enjoy oral sex without feeling like they've lost their innocence. Which is bullshit, really, because when you've seen the look on your partner's face at the moment of orgasm, and they've seen the same look on your face, you're no longer the same person.
Oral sex is also a wonderful way to learn about what your partner enjoys, since you're not necessarily distracted by your own pleasure.