There is a very cool service called WhatTheFont which lets you detect the font used in a logo or image by just uploading it.

For a test I uploaded the Sizlopedia logo and after a quick scan the service gave a list of almost 20 closely matching font styles. Google OS used the Google logo as a test and WhatTheFont successfully detected its font at once.

WhatTheFont supports some common image formats like GIF, JPEG, TIFF, BMP, but you can't upload images bigger than 360 x 275 pixels. It is a useful and handy service that can be used by designers to find the font from a logo or image on the fly.