Here ten sites where you can download free anything that you want for your hand phone:
This site has a very large collection of themes, software and much more. Themes can be sorted by newest first, rating, most downloaded etc. If you do not register, there will be download limits and download delay of 20 seconds.
Though the collection is not very large in numbers, you can find some cool themes including the OS X style theme. For compatibility notations used in the site, you can visit this page
The list is not huge. But has some cool themes like Winter Vista.
One problem you might find here may be the lack of thumbnail view in listing page. You need to click on an item to get the details with thumbnail. But if you have some patience to click on all the links, you will find some good themes.
The pages are easy to navigate. You can sort by rating, popularity etc. You need to register before you can download a theme.
You only need to click on the thumbnails to start downloading.
Large collection of user submitted themes.
This is a German site. The above link will show the translated version by Google. Though the collection is not large, some themes looks good.