Seamless backgrounds can look very nice and are easy to create with Photoshop.

Start with a textural digital image of any kind. It's best when the overall granularity and color content are "conducive to a seamless background.

Then, in PhotoShop, go to FILTER : OTHER : OFFSET and you'll get a dialog box.
Set the offsets for about half the image size in both directions and select "Wrap".

Now use the Rubber Stamp tool with a soft edge brush, set to about 75% Opacity,
and "stamp" over the seams in the picture with adjacent bits of texture.

You now have seamless background tiles.