For pairs, how about:
"Find a partner who you don't know." Nice and simple. No special techniques needed.

For groups, the fastest way is birthdays. If you want six groups, ask those with birthdays in January and February to get together, etc. For four groups, put people together in three-month blocks, and so on.

Having said that, I once ran a meeting in December where I asked people to think of a Christmas carol, then start singing it. People were supposed to meet in groups with those singing the same song. It was delightfully wacky, but a bit tricky with different faiths attending, different musical abilities, etc. Maybe try it with Beatles songs.

Mark Ellwood
GetMoreDone.com

If it's for a negotiation skills course, how about getting them in order by asking them to decide who is the best at something? For instance, place yourself in order of best singer to worst. This would instigate debate and may help with making a point regarding negotiating during the course.

You might check out Bob Pike's 50 Creative Openers. There are great ideas there.

For example, depending on the size of group, you could have famous celebrity pairs on index cards and have them find their match (Lucy/Desi, Fred/Wilma, Laurel/Hardy, etc). For groups you could have bigger casts (think Gilligan, the Skipper, Mary Ann, etc.).

I hope this helps,