Joining Mind-Mapping.Org is an on-line diagrammer that has been around for a while:
Lucidchart is a collaborative diagram-drawing application. You run it from your browser and build diagrams with pre-loaded shapes and images, or with your own images that you can upload. You can share these with others and track who made which changes.
It has several pricing options: Limited free access; $5/month for an individual; or $50/month for groups or businesses (providing 25 accounts).
The $50/month account provides for secure (SSL) connections and sharing images and templates across a team.