Free Photoshop Tutorials

and

Photoshop

Resources, Along with

Free Photoshop

Patterns. Also

Free Flash Games

!.
Tutorial Step 1

Begin by making a new Layer and name it 'Grunge Texture', Set your colors to default by pressing D. Now use Photoshop's Filter>Render>Clouds.
Tutorial Step 2

Tutorial Step 3

Keep repeating the brush strokes until you're satisfied with the outcome, Now goto Photoshop's Filter>Noise>Add Noise (Use about 2-5%)
Tutorial Step 4
Tutorial Step 5

The above is what i came up with. You can Play with the Hue & Saturation to Change colors, Experiment with different Filter Settings to fit your taste.