There are two that I use. For day-to-day, I use one made by Susan Lanci. It's UltraSuede and is SO adorable.
http://www.gwlittle.com/product.php?id=355
The other I use for more dress up occasions is made by Bella. It's a harness & a dress all in one!
http://www.glamourdog.com/havebehe.html
I know, they are both bit pricy. But looking good doesn't come cheap!