I like PhotoForge2 for general editing (cropping, color rebalancing, contrast adjustment.
Also, there is another one called PhotoWizard that does much of the same stuff but also has special effects and the ability to mask and merge layers.
Turbocollage is kind of neat for bunching a lot of pictures together.
Then, Autostich is really great for making panoramas out of many overlapping pictures.
Finally, something like IResize is very nice for turning a bunch of high-memory pictures into something smaller and more manageable.
With Goodreader, I have the ability to email multiple pictures in a single email. thats nice.