Lovely Charts is a diagramming program that is completely online. It is focused on the creation of flowcharts, organisation charts and wireframes.
Lovely Charts uses drag and drop elements to create diagrams that represent flowcharts, wireframes etc. All images can be exported as JPG, PDF or PNG. There is an unlimited number of diagrams that you can create on the site, and you can choose to make each one public or private. You can also allow collaborators to comment on your diagrams.
The ‘Premium’ version of Lovely Charts costs $29 per year. You can also sign up for free, with certain features disabled.
Lovely Charts is available here: http://www.lovelycharts.com/ .