Balsamiq Mockups: Sketching Made Digital (Easy)

I came across a neat little app called Balsamiq Mockups that takes some of legwork out of creating quick ideas and sketches. Mockups offers a pre-made library of UI elements to choose from, all using a hand-drawn style intended to keep the design lo-fi. Within a matter of minutes, I was slapping together a rough representation of some faceted navigation, dragging-n-dropping containers, text, and placeholders onto the drawing board area.

My only issues are that I wish it allowed for custom drawn elements and the ability to detach the UI Library onto a second screen. But other than those, very impressed.