Depends on what you want to do with it. Photoshop and Photosuite are fabulous, but are not free. I have found Photoscape to be of comparable quality, especially if all you want to do is some cropping, red-eye reduction etc.
Here is a download link:
http://download.cnet.com/PhotoScape/3000-2192_4-10703122.html
Note: Only supports until Windows Vista so if you're Mac/ Windows 7 lemme know so I can see if I can get you one that works well.
And Ammeck, don't forget to edit your current location to the US, it still reads UK.