Gimp is a fantastic program for altering images and photos. I use it all the time for my photos, usually for cropping, but sometimes for image manipulation like healing images and removing blobs. It's also good for resizing and re-saving as different file formats.
This has been a lifesaver for doing work on the go. The wonderful thing about it is that you can just share your work with your Google contacts without having to send back and forth. And you can have lots of people working on the same document at the same time! It's brilliant!
This is a no-nonsense PDF maker that basically just adds itself as a printer option when you go to press print. It then just saves as a PDF file. Sorted! :)
I know it's another Google product, but Picasa is a fantastic picture viewing program! It has a nice interface and allows you to basic image manipulation as well as help you organise all your photos. The think I like the most is the slideshow mode of the program which makes your photos look dead pro! Easy to use and just a very small download :)