Title: TwistedBrush Pro Studio
Vendor: Pixarra
Web Site: http://www.pixarra.com/
Type: Raster
Focus: Fine Art
Platform: Windows
Price: $99
Description:
A cross between Corel Painter and Adobe Photoshop. Has a HUGE number of procedural natural media brushes (which scale properly by preserving density) and most of the usual filters and some not supported by PS. This software is primarily intended for drawing and painting, not photo editing as PS / Gimp are.
Examples:
http://help.pixarra.com/m/videos
http://forum.pixarra.com/gallery/

Comment:
I've only just got this software and am so far impressed. Using it in conjunction with a tablet makes it really sing. It will import layered PSD files (don't know about Gimp) but it does not have enough keyboard shortcuts (hopefully these will come in future editions), and those it does support do not mirror PS so there is some relearning required. Incredibly good value for money.