If you intend to blog here at WordPress.com on the blog linked to your username or on any WordPress.com blog then you need to know that the only themes we can use on WordPress.com blogs are found here > Appearance > Themes
There is no FTP access to free hosted WordPress.com blogs and we bloggers cannot install any plugins or upload any third party themes.
See http://wordpress.com/themes/ for the Themes Showcase where there are feature filters in the searchbox that you can use to narrow your choices.
Note also that we Volunteers and Staff do not assist with theme selection as it's subjective decision making process and there are over 220 themes. We are focused on providing assistance with support issues only.