Gimp
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Handy Tweaks To Make GIMP Replace Photoshop | How-To | Smashing
GIMP is the favorite graphics editing program of many designers and graphic artists. It is free and compatible with Windows, Mac and Linux (the two big reasons for its popularity). It has a wide array of features, as well as plug-ins, filters and brushes.
Layer Effects
This is a series of scripts that implement various layer effects: Drop Shadow Inner Shadow Outer Glow Inner Glow Bevel and Emboss Satin Color Overlay Gradient Overlay Pattern Overlay Stroke Some effects can have contours (a.k.a. curves) and noise added to them. Effects can either be applied on a separate layer, or be merged into the active layer (which in some cases gives better results). Tested with GIMP 2.4.2.