From Second Life Wiki
Great set of software tools ---- except for one glaring omission! Ok, Photoshop is a VERY expensive piece of kit, but some of us are lucky enough to have it already (I use the rapidly ageing PS7 for Mac) so it should be in the list? GIMP is great as a free program, but Photoshop is the original and, many believe, still the best. It is probably true to say that for most clothing-making textures, PS7.1 is the minimum level required, certainly for such items as tattoos. (Tid Kidd)
Another omission: For Macs (There is a version for Windows, but I have not tried it), StarfishX is made to make desktop patterns. They are random (you can select the seed number, but there is no way to predict the result) and tile perfectly. By the editing of the color palette, you can get nice wood grain. It makes TIFF or JPEG, so you will have to convert the files to PNG or Targa before uploading.