This is an updated version of the list of image editors and converters carried over from the old forums.
Sometimes you don't need to fire up Photoshop to crop or resize an image for uploading to your webpage. I therefore have compiled this (by no means complete) list of free image editing software.
I haven't got around to trying all of these yet, the information is mainly what I have gathered from websites and forums etc. If anyone has tried any of these, or have any to add to the list then post them on this thread.
Of course, this list only contains software where Windows versions exist, so if anyone can help make this multi-platform, then please add your favourites to this thread.
PowerBatch 6.0 - 1.3MB
Batch renaming, resizing, converting, printing, rotating, colour adjustment, cropping.
Crop with aspect ratio confinement.
Built-in FTP client!
All program files are contained in a single folder.
Converts JPEG, GIF, PNG, TIFF, BITMAP and JPEG2000.
Supports animated GIF and multipage TIFF.
Add multi-line text.
Stamp photos with EXIF data.
Paint.net 3.36 - 1.6MB
Clean GUI with tabbed document interface.
Effects filters, image adjustments (brightness, contrast, hue, saturation, curves, levels).
3D Rotate/Zoom effect that makes it very easy to add perspective and tilting.
Powerful drawing tools (clone stamp, recolour, splines, Bezier curves, gradient tool) akin to Photoshop.
Powerful selection tools and selection manipulation.
Developed with help from Microsoft.
Active Online Community.
Requires 22MB .NET Framework 2.0 to run.
Layers and transparency support.
Pixia 4.3d - 4.8MB
Photoshop Filter support.
TWAIN device support.
Native support for Wacom tablets.
Layers, transparency and masks.
Image adjustments, filters.
Photofiltre 6.3.2 - 1.6MB
Free for non commercial or educational use.
Multiple images open at once.
Image adjustment functions.
Vectorial selections, transparency masks.
Drawing tools (pipette, displacement cursor, fill bucket, aerosol, brushes, blur, cloning stamp, smudge and magic wand)
Adjustment functions (Brightness, contrast, dyed, saturation, gamma correction)
Many plugins and more than 100 filters.
FastStone Image Viewer 3.6 - 4.0MB
Free for home users.
Convert major formats (inc. PSD and many digital camera RAW formats).
Lossless JPEG rotation and cropping.
EXIF and colour profile support.
Resizing, flipping, rotating, cropping (with aspect ratio/size confinement), sharpen/blur.
Colour, gamma, contrast, RGB level, sturation adjusting tools.
Compare images side by side.
Batch image converter/resizer.
Supports animated GIF and multipage TIFF, PDF.
Image management, including tagging.
Watermarking, red-eye removal.
Contact sheet, executable slideshow, image strip creation.
Versatile screen capture, Dual-monitor, TWAIN scanning support.
Xnview 1.95 - 3.7MB
Free for non-commercial, educational and non-profit use.
Utility for viewing and converting graphic files.
Imports 400 graphic file formats.
Exports 50 graphic file formats.
Copy, cut, resize, rotate and crop (lossless for JPEG).
Brightness and contrast adjust.
Modify number of colours.
Filters and effects.
Contact Sheet and TWAIN support.
Supports animated GIF, ICO and multipage TIFF, DCX, LDF.
Compare image side by side.
Batch convert and rename.
GIMP 2.6.3 - 15.0MB (Win32 version)
(gimp-win.sourceforge.net Windows version)
Highly configurable GUI, menus, keyboard shortcuts.
Probably the best open source contender to Photoshop.
Requires GTK+ 2 runtime environment - 5.5MB.
Painting tools including Brush, Pencil, Airbrush, Clone stamp, Healing tool.
Perspective tools, image distortion correction.
Multiple images open at once.
Layers and (alpha) channels.
Selection (inc quickmask) and transform tools.
Advanced scripting capabilities, over 100 plugins available.
Animation inc. MNG support.
Supported formats include bmp, gif, jpeg, mng, pcx, pdf, png, ps, psd, svg, tiff, tga, xpm.
Advanced hardware support (tablets, mouse, monitor).
Difficult to get used to GUI layout.
GIMP Portable 2.6.3 - 16MB
Version of the GIMP that can be run from CD or Flash drive (Windows only).
All necessary files are installed including the GTK runtime environment.
IrfanView 4.23 - 1.3MB
Free for non-commercial use.
Huge array of supported file formats (inc. movie, audio, multipage TIFF and saving ICO).
Slideshows saved as EXE, SCR.
EXIF IPTC support.
Many plugins available and support for Adobe Photoshop Filters.
Batch scan support.
Extract icons from EXE, DLL, ICLs.
Lossless JPG rotation.
Image Analyzer 1.3 - 1.3MB
Automatic brightness, contrast, gamma and saturation adjustment.
Conventional and adaptive filters for noise reduction, edge extraction etc.
Retouch tools (inc. red-eye removal)
Out-of-focus and motion blur compensation (very good by the look of the sample pics)
User specified filters.
Resize, rotate, crop and warping of images.
Scanner, camera and printer support.
Many file formats supported (inc. saving ICO).
Distance, Fourier and discrete cosine transformation, Morphological operations (your guess is as good as mine!).
Math expression module for creating and transforming images.
PhotoPlus 6 - 19.5MB
Creative Tools - paintbrush, airbrush, clone, smudge and erase.
adjustable brush settings include size, shape, softness and fade.
Adjust brightness, contrast, sharpness, color hue, saturation, remove red-eye.
Layer Effects - Bevels and drop shadows. Add to images without affecting the originals.
Deform tool lets you rotate, resize, skew, reshape and add perspective to selection or layer.
Add editable, deformable text and apply layer effects.
Create animated GIFs.
Image slicing for HTML pages.
Export Optimizer - View up to four simultaneous previews with varying file size and quality.
QuickShapes - Including speech bubbles, starbursts and spirals.
DrawPlus 4 - 19MB
Vector art software.
Drawing & Sketching - QuickShapes, Natural Curve Editing and Curve Smoothing.
Backdrop Wizard - Easily add abstract or themed backgrounds.
Studio Resources - Hundreds of pre-set lines, fills, transparencies and fonts.
Colour Selection - Apply colour fills to backgrounds, shapes and your own drawings.
Animation tools - onion skinning, backgrounds, overlays and frame management.
Blend tool - Automatically 'morph' two images into one another.
Transparency effects for photo-like realism and quality.
Add watermarks and borders.
Colour Schemes - Define colour sets as shades of a base colour.
Editable Envelopes - Stretch and squeeze objects or text.
Add text and convert to curves for editing.