When I first got brave enough to post something online, I just used the text editor that lived within my photo editor to put my name and some credits onto the image. After a while this got old, plus I kept making typos which got really bothersome, so one day I gave in and bought a watermark.
There are a ton of sources out there for purchasing a watermark, plus tutorials on how to make your own. Personally, I am lazy and very into that whole instant gratification thing, so it was much easier to have someone do it for me. ;-)
I got mine from Mama Dini's Digi-Sig Diner. She was super fast and efficient, and very helpful in all ways possible. She has so many styles to choose from (from which to choose), I had a difficult time, but I finally decided on this one:
When I first got the file from her, I told her I'd post back with an example of a card using her watermark, and I am finally getting around to doing that. So Mama Dini - here you go!
For future reference, I have also added a link to her site in my Side Bar. Thanks Mama Dini, for making my crooked stuff a little more professional-looking! ;-)