Tumblr is a very popular and free to use blog platform. Tumblr is widely used by bloggers and companies for their blogging needs as well. There is a variety of free themes you can choose from, however a lot of them have the "free" look. Serious bloggers and companies that use Tumblr buy themes for a few bucks which gives their blog a much more professional feel.
Below are some popular paid Tumblr themes for you to check out.