When I go to my own profile, only five communities are shown under Communities.
Why aren't all displayed? For one there is an, about, 1340 pixels empty space below the grouping, and the hassle of going to the bottom of the page and navigate trough various pages to find the community I am registered at seems rather non-user-friendly (easier ways are shown in comments and answer).
At least have a “show all” or the like option.
As an added note: I have more focus on the feature-request then alternative ways as I think it is the more intuitive and user friendly approach.
By all means; keep the other ways, but why not have it where I guess a lot of people both remember to have seen a list and likely is a place they go to look for it? At least my thought is that Profile is a natural place to look for it.
It continues even further down. (And, yes, that picture is rather user-unfriendly as well; but as an afterthought it is proving the point.)