When I tried Little Snapper from Realmac Software I was very impressed with the annotations included. They are much more professional looking than the annotations included in Skitch.
I don’t need the other facilities this provides but I did want this style of annotation. In the end I realised that I could just make my own in the ever-fantastic OmniGraffle as a set of stencils I could drag onto images. The resulting annotations are shown below and are available for download through the Graffletopia website.
Software