Whether you are away from your own machine or want to save money on expensive photo editing software there are some very powerful and free online tools to help you edit you photographs directly from the browser.
Picnik, recently acquired by google is clean and feature rich. Picnik seamlessly combines easy to use automated functions alongside some more advanced tools like a Histogram and an Unsharp Mask. Picnik is aimed at the general user and is mainly designed to prepare images for web based application. Most base features are free but some effects and tools are only available at a cost with the premium version.
Adobe has an online version of Photoshop called Photoshop Express that is perhaps a little more serious than Picnik. Here we are presented with editing techniques that are a little more photographic in nature.
Both provide various options for output and upload to popular social media sites. Photoshop Express aims to incorporate itself as a social network by allowing you to share albums and view albums of other Photoshop Express users. Both are excellent tools suitable for beginner and advanced image editing.