The top command gives the list of processes running in the memory which can be sorted on the basis of memory consumption using the 'n' option.
To get the list of zombie process, use the command "ps aux". One of the columns gives the status of the process. It is column no. 8 in RedHat Linux. A value of 'Z' in this column indicates it is a zombie process. Using the kill comman, you can killl the process.