This list contains various resources that I have personally used on many sites. The themes are completely free although many of them require that you keep the link in the footer which isn’t too much to ask, after all, it is someone’s hard work.
Below you will find a few links to extensive and useful free or open source themes for WordPress and some are even used for normal web design…
My personal favorite would have to be smashingmagazine.com –100 Excellent Free WordPress Themes
With this large collection you are bound to find something to suite your style and blog and or website.
Veering away from WordPress…
Open Source Web Design – Browse Free Web Design Templates -There are currently 2080 free designs on Open Source Web Design for you to choose from.
Your Business Blog
Your business’ blog doesn’t have to look boring or childish. If you’re going to use your blog as a tool to promote your business, you need it to have a clean, professional, corporate look. Here’s a round up of 20 of the best free corporate WordPress themes available. Preview them and if you find one of your taste, go ahead and download it here.
Here you can find a small but powerful set of designs that would compliment your blog nicely.