FilterForge: full 8/16/32 bits per channel nodal seamless textures and custom filter plugin (and stand-alone) for Photoshop plugin compatible image editors. A library of more than 10.000 effects and textures all free for download. FilterForge comes in four different flavours: basic($149), standard ($249), professional ($399), and professional subscription ($29). Works great with Photoline.
http://www.filterforge.com/
Genetica: powerful nodal seamless texture generator. Comparable to FilterForge, although somewhat more geared towards 3d artists. Basic ($149), Pro ($399), and Studio ($849).
http://www.spiralgraphics.biz
Free Genetica based texture generators:
http://www.spiralgraphics.biz/ww_overview.htm
http://www.spiralgraphics.biz/viewer/index.htm
Blender has a wide range of nodal texturing built right into it.
Photoline, arguably one of the most powerful image editors around, also offers a procedural seamless texture editor. Although it is limited to 1024px, combined with the non-destructive layer-based editing many seamless textures can be generated. Combine this with FilterForge or Genetica!
59 euros. http://www.pl32.com
TG - tg is a texture generation / synthesis tool. use it to create beautiful textures for demos and intros or just for fun.: http://www.blackpawn.com/dev/tg.html
Free.
Seamless Texture Generator: http://www.seamlesstexturegenerator.com/
$40
NeoTextureEdit - NeoTextureEdit is an open source (GNU LGPL v. 3) easy to use graph-based procedural seamless texture editor. Using continuous basis functions it can generate arbitrary resolution images without quality degradation.
http://neotextureedit.sourceforge.net/
Free
Texture Studio is all you need to produce professional quality textures for use in games and tiled backgrounds. Texture Studio includes a set of integrated tools, all extremely useful for creating high quality seamless textures. Texture Studio is so easy to use, a photograph can be converted to a smoothly tiling, seamless texture with a single click.
http://www.blitzbasic.com/Community/posts.php?topic=46368
Texture Maker is a seamless texture generator and designer. The application contains everything needed to create seamless textures for use in 3D rendering packages, game development, web graphics, image and video editing.
http://www.texturemaker.com/tour.php
Basic (30 euro), Advanced (65 euro), Professional (100 euro)