Here’s a quick how-to for making those cool grainy textured web backgrounds using Photoshop starting with a square 100px x 100px, for example:
1. Fill with the color of your choice
2. Filter > Noise > Add noise 7%
3. Image > Adjustments > Desaturate (You’ll be adding your color back in later. This step is necessary to get an even grain pattern without extraneous bits of color.)
4. Create a new layer filling with the same color of your original choice
5. Set the opacity to 60%
6. Try changing the layer styles for different effects using multiply, soft light, etc.
You can see another example of a grainy textured background on this blog!