Find out which users are hogging the most disk space on our data server

We are supposed to store our ongoing projects on a rather small (~4TB) data server. Not surprisingly, it is constantly overflowing and people need to move off less recent files manually. Is there an easy (aka standard command-line) way to find out which users take up the most space in a directory? i.e. summing up the size of all files in a directory and all sub-directories belonging to each user? Edit: ideally not following symlinks