I love the Gimp as well and have used it for years.
Another free editor for windows is Paint.NET
It does not have all the scripting and filter function of The Gimp, but definitely can do a lot, and worth checking out.
Don't forget about IrfanView
. Although it is primarily a viewer it does ahve some cool editing features. It also has very robust metadata features.
Oh, and then there is XNVIEW
, free also, and great for batch resizing.
I personally have found my investment in Adobe's products very worthy.
It is such a great community and very high level software.