Not exactly developer related, but this is the best free lightweight imaging tool I've found. I've been using it for the last year, but this post on download squad reminded me that I should post it here.
[Via Download Squad]
Okay, it doesn't take much to be an "MS Paint killer," and probably any one of Paint.NET's features could have netted that title. Paint.NET could better be described as a simple image and photo editing tool that sits somewhere in the middle ground between MS Paint and, say, Paint Shop Pro. It supports layers, history, common effects, and familiar tools like magic wand, clone brush, and recolor. As of version 2.5, released on Saturday, Paint.NET sports more selection features, spline and curve tools, a 3D zoom/rotate tool, improved font rendering, faster performance, lower memory usage, and an extensible file format API. Paint.NET is an open source project, distributed under the MIT license, and is a small download if you already have the .NET framework.