You have to run:

 

ps aux | sort -nk +4

That will print you a list of all the running applications and it wil sort them by the 4th column (memory)

The same can be applied for CPU, Virual memory etc. Just change the -nk +4 value to +3 +5 etc. Very usefull trick for administrators. In openvz for example, where virtual memory is in fact normal memory, you might want to take a look what program uses the most virutal memory.

Thanks