Here is a fun design. I love the grunge effect. It's stylish and modern and I love the randomness of it.
Here are a couple of examples some grunge style calling/business cards.




So, how do you make a cool grunge effect?
First, you need a texture to draw from. You can make your own by taking a picture of something with texture, such as a rock and importing it into a photo editing program, such as GIMP, which is free and extremely powerful.
Next, use the select by colour tool

.
Choose a texturous part of your image and click. If you are getting too much or too little selected, simply adjust the threshold accordingly.

. Once you have selected the portion of the texture that you want, copy the selection (ctrl+c), open a new layer

(the white button on the bottom left) and paste your selection on the copy (ctrl+p). Then, click on the eye beside the original image to make it disappear. To make your selection grayscale, click on colours, then desaturate. You can also give your grunge layer a bit of transparency, so it blends into your background better (in the layers dialogue, make sure the grunge layer is selected, then move the opacity arrow to the left).