Paint Shop Pro. I upgrade every year.
- It is far cheaper than Photoshop but has the same key functionalities.
- It accepts all the Photoshop add-ins if you have or buy any.
- It has a very easy to use interface.
- Powerful layering capabilities.
- A very nice in-screen help system that is context-sensitive and can be turned on when you start working in an area you not familiar with or have not been into for some time.
GIMP is very capable as well, but has a fairly steep learning curve and only comes really into its own once you have hunted down a bucketful of add-ins to improve the workflows in areas you are interested in.