This site has many choices to choose from. They have everything from glittery ideas to birthday themes.
All you have to do is go to the website select a category you like and find which one is your favorite. After you find which one you like you can go to your blog get the HTML gadget and type the HTML that it gives you at the bottom of the page. Keep in mind that this is not just a girl website. It has girly backgrounds, but men backgrounds are there too.
