@MoodleDan sent in a link last week with four free Moodle themes.
EduMoodle – a clean, blue theme with the standard Moodle icon set
Junction – this funky use of color and images will make your Moodle pop off the page.
Pretty Simple – this is one of my favorite themes which accomplishes a stark and spartan layout. Moodledan mentioned that it was created to be consistent with an existing Joomla theme that a school had already implemented;