Image editing tools

Gimp

http://www.gimp.org/ - which is a free opensource program similar to photoshop. It's got lots of tricks, possibly too many as it can confuse sometimes. But if you're after a good solution and don't mind the leg-work it is definitely worth it.

Photoshop Express

https://www.photoshop.com/express/landing.html - Adobe (the people behind Photoshop) have released a cut down version of Photoshop on the internet. It is free (and requires no download) and incorportes a social networking system and galleries for your work similar to Flickr. Of course it doesn't have all the features of the real thing but it is surprisingly good!