1. Use a social event
Weddings, funerals, a coming of age ceremony, the crowning of a new king, the list goes on. Give each PC a tie into the event, and then bring them together with something like the reading of a will, the quest for a perfect wedding gift, a trial of adulthood that involves the group, or the new king's first order to rid the land of some trouble.
2. Victims of circumstance
I once had each of the players name a relative...as the campaign began, I told them they were each looking for their lost relative and it had led each of them into the same particular town...eventually, as they crossed each others paths in town, they joined forces (gradually, not all at once) and discovered at the conclusion of the adventure that their relatives were turned into ghouls. The adventure brought them all closer because they now had something tying them together.
3. Home sweet home
Just let them start in the same town, and put the town in danger. Who wants to let their families go unprotected?
4. It's a clan thing
I had a great success when I asked all the players to choose the same race. It could be any race they wanted, but it had to be the same one. I also had them choose their classes like normal, but had them all put one level of another class as their 1st class level.
When my players chose dwarves as the race, I told them to all put one level of barbarian as their first character level, and placed them in the snowy mountains. They still got to choose their own class as their 2nd level, but the fact that they were all part of a barbarian dwarf clan really added a lot of flavor right at the beginning of the campaign.
5. Divinations
I have mixed feelings about divinations. I think they get overused sometimes, especially at higher levels. But, the pursuit of some relic, or a simple quest can always be a good intro for a campaign.
Ultimately, I think a combination of any or all of the above options can make for an excellent start to a campaign.
Good luck with yours!