[spuiszis]

In addition to your typical Outlook, i0S contacts, etc., there are a services that come to mind:

Plaxo (Plaxo.com founded by Sean Parker) has been around for awhile. I used this for some time but have recently discontinued my account.

Brewster (https://www.brewster.com/) is new on the block and I also think Fred Wilson had a blog post on them earlier this year.