GIMP - GNU Image Manipulation Program
GIMP, often touted as a Photoshop replacement by its fans, allows you to create and edit images and photos. It has the usual facilities found in many commercial paint programs such as a variety of paint tools (Brush, Airbrush, Pencil, Clone, custom brushes and patterns, etc), full alpha channel support, layers and channels, transformation tools (rotate, scale, sheer, flip), multiple undo and redo, selection tools (rectangle, ellipse, free, fuzzy, intelligent, bezier, polygonal), animation support (including MNG), numerous file formats (BMP, GIF, JPEG, MNG, PCX, PDF, PS, PSD, PNG, SVG, TIF, TGA, XPM, etc) including conversion between different file formats, and so on. Supported systems include Windows, Mac OS X, Linux, FreeBSD and Sun Solaris. This is an open source program.
Google Picasa ( Get photo software from Google )
Picasa is a photo editing program that allows you to edit and organise your pictures on your computer. You can add visual effects to your digital pictures, write captions, pan, tilt, zoom, crop, eliminate red eyes, change the contrast, colour and enhance them. Other features include the ability to create slide shows, upload your photographs to your blog or website, burn them to CD or DVD, make a desktop image, create a screensaver, etc. The software is available for Windows and Linux.
Tux Paint
Tux Paint is a drawing software designed for young children. It has cute looking buttons, sound effects and a mascot that encourages children as they use the program. Supported systems include Windows, Linux, Mac OS X, FreeBSD and NetBSD.
Paint.NET
Paint.NET is an image and photo manipulation program that supports layers, unlimited undo and redo, special effects, drawing tools (tools for drawing shapes, splines, Bezier curves, etc), etc. It runs under Windows 2000, XP, 2003 and Vista. It requires the Microsoft .NET Framework (hence its name).
Inkscape - open source scalable vector graphics editor
Inkscape is a scalable vector graphics (SVG) editor. It is open source, and versions are available for Windows 2000, XP, 2003, and OS X.
DrawPlus 4
DrawPlus 4 is a drawing and painting program. It supports the GIF, JPEG, BMP, PNG, WMF and EMF graphic file formats. The program is no longer maintained. It supports Windows 95, 98, 98 SE, ME, NT 4.0, 2000 and XP. You have to register with your email address to use the program.