Kiss. Fondle. Nipple play. Some oral. It's what has worked for me and my lovers, and if it ain't broke, don't fix it.
Could you be a little bit more specific about why you're asking the question? There are a lot of different things that can qualify as "foreplay": teasing, tickling, massage, dirty talk, illicit footjobs at a fancy restaurant, sexting, or even just the right look or word or smile or smell. Are you running out of ideas with your partner? Are you trying to settle a bet? Are you trying to correct the definition on Wikipedia? Why, in short, do you ask?
I generally get backhanded across the face and throat-fucked against the nearest wall. Opinions are like arseholes my friend; everybody's got one but you don't necessarily want to be exposed to it.
If you want relevant feedback, you should ask a less vague question. I don't even know what gender you are and what gender you fuck.