The Directory is a pretty important place if you're planning to connect with other users or promote your account.
You can access the directory by clicking DIRECTORY in your dashboard or visiting www.tumblr.com/directory
Once there, you can click a subject/topic and find blogs. When I clicked ANIMATORS above I received a drop down menu with a list of other topics.
You can list your own tumblelog by clicking GET LISTED or recommend a blog (or have someone recommend you!) by clicking RECOMMEND +.
This is a good way to find celebrities and personalities (when I clicked COMEDIANS I found Aziz Ansari and Rob Hubel) and have yourself found by others (so you can build a community).
Introducing the new Tumblr directory, Tumblr staff blog