If diamonds are a girl's best friend, then bookmarks are authors. They are by far my favorite promotional item. Why you might ask? Because they are very affordable to get designed and printed up. With mine, I keep it pretty simple. Typically my book cover(s) is on the front, and the synopsis is printed on the back. I also make sure to have contact info located somewhere on it so that readers can find me.
Several business offer both for reasonable prices. However, my favorite is www.overnightprints.com. Another printing site I love is vistaprint.com. Over the last few years I've come to find out just how helpful bookmarks can be. Not only are they great for slipping into conversations, you can also leave them in stores, libraries, etc. (with permission of course). Bookmarks are great for drawing visibility--especially if you have an eye-catching design. I highly recommend using a professional graphic designer!
Remember, no one's gonna push you like YOU! Branding is a key factor to success!