On-Screen Ruler - lightweight, free, semi-transparent ruler
ToolSalad.com - A Curated Directory of 204+ Online Marketing Tools for Startups, Bloggers, SEOs, and Marketers.
Bluegrams Screen Ruler - A lightweight and configurable ruler tool for Windows Desktop.
Mr. Free Tools - The Most Advanced Directory of Free Tools
Pixus - Pixus is an AIR pixel ruler application, a handy tool for web and interface designers.
StartupResources.io - Tightly curated lists of the best startup tools