Embedded Linux Primer

pstree - displays the relationship between child and parent processes
-a displays process args
-h highlights the current process tree
-H highlight a given process
-u displays the user
-p shows the pid

ps - display processes
Have you ever read the man page and tried to figure out all the legal possibilities? :)
My favorite:
* ps aux (display every process on the system)
* ps axjf (display a process tree)
* ps eLf (display threads)
* ps axms (display threads w/ signal masks)

pgrep - look up processes (instead of ps | grep)
* pgrep -u user - show processes for user
* pgrep -l (show process name as well as PID)
* pgrep -f (pattern match)

Nice utils to play with and master!