Here's a quick and intensive way to watermark all of your hard, hard work. You're basically making a brush in Photoshop that you can use at any time to stamp your photos as your own. It takes a little a set up the brush, but once saved, you just click and bAM! It's all yours.
^ These are clickable thumbnails, so click them, save them and print them.
Scanned by me, from a photocopy of Photoshop User Magazine.