On-Screen Ruler - lightweight, free, semi-transparent ruler
Design Details Podcast - A show about the people who design our favorite products.
Bluegrams Screen Ruler - A lightweight and configurable ruler tool for Windows Desktop.
Tentative - Podcast about product design hosted by Thoughtbot designers
Pixus - Pixus is an AIR pixel ruler application, a handy tool for web and interface designers.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.