Top - find those greedy processes using Terminal

Want to find those greedy processes? Wanna bet it's Firefox? Just kidding. Sort of. Just run this at the Terminal window (Applications folder | Utilities folder | Terminal, or just launch Quicksilver and type "Terminal"):

top -ocpu

This will list all your running processes by CPU utilization. The offender will be at the top.

Press "q" to quit. The PID can be used to kill the process as well, but that's probably only for more advanced users. I use this technique occasionally when I need to SSH into my mac box and kill some process that's sucking on the resource pipe a little too hard :)