There are three ways I can think of to overcome the appearance of tiling. The simplest is to use a bigger texture. If you have a texture that is half the size of your map or larger then the tiling won't be visible. Or, you can mix another texture with a different resolution with your original texture. This can be done with a simple blending mode changes (overlay is usually the way to go, especially with stone), or with a mask on the top texture that reveals the bottom texture in places where the tiling is most obvious.

The toughest way is to find or modify your texture so that the features that make the tiling obvious are minimized. Depending on the texture, this may be impossible, but it can usually be done. I think it was Redrobes who posted a good tutorial on how to make seamless textures a while back. You might look around for that if you decide you need to modify the textures.

Finally, a good source of texture resources is CG Textures. They have thousands of high quality, high resolution images ,and their license permits royalty free use for any application except scrapbooking (I have no idea why that particular restriction).