Irfanview is great for working with. Although it isn't an all out image editor in its own right, I use it in conjunction with Photoshop and the GIMP. There is a plethora of plug-ins for it to do just about any filter, and, unlike GIMP, it has a
very simple and intuitive interface. Besides that, for web purposes a good image optimizer is almost a necessity. I had one that I had on trial that worked well, but it is on a different computer in a different house, I'll see if I can remember what it is.
EDIT: My optimizer was
xat.com's image optimizer tool.