hmmm... actually, it seems there are alot more communities than what first show up. looks like the default list is the "rank" selection, whereas if you choose "subscribers" or "new" instead, the lists change and there's different stuff in there - and there's also alot with less subscribers that you can find if searching for a particular word. (i.e. "music" brings up a shitload of communities that don't appear in any of the other lists.)

looks like can either go directly to a community page or the My Communities page which gives a feed of content from the communities you've subscribed to.