Really it's just 711chan/7chan/and a bunch of other kusaba imageboards run by 12 year olds. Other places are pretty serious.

The most active "serious" imageboard I can think of is 420chan, which has a nice community. Memes are never really spread around, only in /b/. There are also small communities like 1chan's /rail/ or the various iichan boards that are pretty cool.