One of the things I learned about in Matt Kloskowski's "Layers: The Complete Guide to Photoshop's Most Powerful Feature" is how to use a clipping mask (the definition of which always eluded my comprehension)to fill text with an image.
Without going into a complicated explanation:
1. Create a new blank image.
2.Use the type tool to put nice fat text on it that will leave enough room for your picture to show through.
3. Open up an image from which you want to choose an area to fill the letters. Arrange your screen so that both images show. (Go to Window>Arrange>Float in Window at top of screen.)
4. Use the move tool to drag the photo over the text layer.
5. Go to the Layers menu and click on "Create Clipping Mask". All of the picture will disappear except what fills the letters. You can click on the picture layer and use the move tool to move it around so the part you want fills the letter.
(Stroke and drop shadow were added in Photoshop's Layer Style menu)