Picasa
On my old laptop I occasionally used Picasa for organizing my photos. When I got my new laptop I found that there's an upgrade edition -- and it's fantastic! Okay, I'm not a big fan of the organizing part. Maybe because I'm still kind of old school, I think that part could be better (like the ability to save changes to the original without making a copy), but it's got some great better-than-minimal manipulation tools including color removal based on chroma filtration (so it's like using filters with B&W film), graduated tints, shadow/highlight control, and more. First button to try is I'm Feeling Lucky (remember, its a Google product) for the best "instant fix" I've seen in any product.
By the way, it's tightly integrated with another great product, Hello. That's the software I use to post the pix in this blog. That's how I found the Picasa software. It was recommended after I downloaded Hello for pic posting. Blogger seems to recommend some really good software. That is how I started using Firefox, too.
