One way, is to have them hear of, or read a posted notice asking for adventurers to apply... They go in and give their spiel, along with some NPCs, and then the person in charge selects the NPCs for the job, leaving the PCs to their own devices... Naturally, in "applying for the job", they have already "introduced" themselves.
Player reaction: "Well!... THAT never happened before!"
Another unusual way is to start them off in the "MindWipe" adventure, where the game begins with them strapped to a table, with a needle in their arm, and with no stats, memories, nor equipment. I have run this, several times, to good effect. If you're interested, you can see a Sci-Fi version of it, here:
http://anch_stevec.crosswinds.net/mindwipe.htm
Of course, anything that brings PCs into the same village, hamlet, town, or even a small city will also work. Once there, something happens that brings them all together. Mugging, siege, stampede, etc.