Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

Listography - Create your lists, preserve your story, and stay inspired.

Eventbrite - Discover Great Events or Create Your Own & Sell Tickets

List Challenges - Earn points for your life experiences. Find lists that interest you, and mark off what you've done.

Bigtent - BigTent is a web-based organization and communication portal for groups.

Bucketlist.org - Log and catalog all the stuff you want to accomplish before you expire.