hey FingersEddie,
I never really considered creating decals for fellow modelers, but I'm sure there are some websites that provide custom decals. It really isn't that difficult and it would save you a few bucks to create your own, assuming you have an ink jet printer or access to one. I ordered my decal sheets from Papilio based in Texas http://www.papilio.com/ (I believe Testors makes them as well). A pack of 10 sheets sized 8"x10" was $11.25US, but shipping costs to Canada was almost double the product price.
I used the clear type, but white decals are also available. There are advantages and disadvantages to both. With the clear you don't have to trim the decal right to the image, but since ink jet printers don't print white ink (at least not that I know of, but someday I'm sure that will change) you have to place the decal over a white background to get it's true colour. With the white decal film, you don't have to worry about this. You will have to trim right up to the image to elimate excess white. I suppose you could paint up to the image once it is on the model. Another method to try is introducing the background colour of the model around the decal while it is still on your computer screen and do some blending afterwards on the model.
For software I'm sure any program that is used for photo editing will suffice. For these decals I had the images set at 1200 dpi and not until at the very end before printing would I shrink them down to the required size - test print on plain paper to determine exact size.
Other items needed is can of fixitive spray which is available in craft shops - I used a matt finish from Krylon. This is sprayed on the decal once the ink is dry. As an extra measure, once the fixitive was dry, I brushed on some Future acrylic just to make sure the ink was sealed on the decal film. After this dries they are ready to use like any other water slide decal.
Anyways, here is the finished knight ... next comes the horsey