A friend of mine just asked me how to make an image or a logo look like a sticker when used as part of a digital graphic. Here's the steps I use to create the sticker effect using Photoshop (CS3).
Start with your logo, flatted into a single layer.
Go to Layer > style options >stroke
Add a stroke to the thickness you'd like to see the “die cut” of your sticker shape. The stroke color doesn't matter, so make sure to use a color you can see for sizing.
Duplicate the layer, then merge the two layers together so you have a single layer with the stroke permanently incorporated. This will be the die cut shape of your sticker.
Click the checkbox for “preserve transparency” for this layer. Fill the layer with whatever background color you'd like. If you have holes in the inner area of the shape, fill them in as desired.
Now you can add a shadow or even a puffy sticker effect by playing with your layer options under the drop shadow or bevel choices. Remember You don't want to add too much of a drop shadow or your sticker will float.
There ya go! Play with the layer options as well as your stroke thicknesses or even textures to create various effects and sticker looks.