Personally I'm not too interested in having IDE integration so...
Wireframing
* Mockingbird (http://gomockingbird.com) - Built on Cappuccino, best designed of the bunch
* Napkee (http://www.napkee.com/) - Flex
* Hot Gloo (http://www.hotgloo.com/) - Just a web app I believe
* Pencil Project (http://www.evolus.vn/Pencil/) - Firefox add-on
* Several more wireframing type apps...
Mockup feedback
* Mocksup (http://mocksup.com) - Make your mockups clickable (Full disclosure, I'm co-owner)
* Notable (http://www.notableapp.com/) - Mark up websites and mockups with comments
* ConceptShare (http://conceptshare.com/) - Same
* Several others that focus on just mockup feedback, not much differentiation
Peldi
Wireframing
* Mockingbird (http://gomockingbird.com) - Built on Cappuccino, best designed of the bunch
* Napkee (http://www.napkee.com/) - Flex
* Hot Gloo (http://www.hotgloo.com/) - Just a web app I believe
* Pencil Project (http://www.evolus.vn/Pencil/) - Firefox add-on
* Several more wireframing type apps...
Mockup feedback
* Mocksup (http://mocksup.com) - Make your mockups clickable (Full disclosure, I'm co-owner)
* Notable (http://www.notableapp.com/) - Mark up websites and mockups with comments
* ConceptShare (http://conceptshare.com/) - Same
* Several others that focus on just mockup feedback, not much differentiation