On-Screen Ruler - lightweight, free, semi-transparent ruler
Img.vision - Image hosting & video hosting for eCommerce sellers
Bluegrams Screen Ruler - A lightweight and configurable ruler tool for Windows Desktop.
UploadHouse - Thumbnail and resize your photos and images
Pixus - Pixus is an AIR pixel ruler application, a handy tool for web and interface designers.
ImageVenue - ImageVenue is a great online hosting service that allows uploading pictures for showing creative works with a simple-to-use technique.