Twitter Bootstrap and Omnigraffle
Historically, I have not been a huge fan of front-end frameworks, especially in production sites. However, I quickly became a fan of Twitter Bootstrap when I needed to prototype a web application that was certain to go through many iterations before seeing daylight. When you're trying to hammer out functionality and user flows, faster prototyping benefits everything. Bootstrap's design patterns are not necessarily unique, but they are well made and look great.
I've used Omnigraffle for wireframing on and off for the past few years. It was Viget Lab's original Boostrap stencil made in 0000 that really hooked me into Omnigraffle. Now they've released an updated stencil for Bootstrap v2.2. The amount of time you can save with this combo is truly epic. Muchos gracias, Lance, Elliott, and Todd at Viget Labs!