Mocklinkr is another new design mockup review service to hit the web. This one adds a little twist, however, that might be pretty useful. After you upload images of your designs or wireframes, Mocklinkr let's you create clickable sections on the image linking to another image. This let's you do very simple click-through prototypes to change state and navigate between pages. In a way, this seems a bit like the Berkeley GUIR Denim tool, which is sadly no longer available at the GUIR site.
The video above shows how it works. Jump to 0:30 for the demo. The prototyping is not as sophisticated as using standalone wireframing software or something like Balsamiq, but the approach should be very simple and friendly for people who don't want to bother with software. It allows you to use your own images and adds the online annotation and review features. It's nice to have so many different service options these days.