Htop is a process manager that builds on the functionality of top. It allows you to view available memory and CPU usage as well as kill and manage running processes. It integrates quite well into the system manager Conky.
Htop has a few features not found in top. First of all, the interface is more appealing, and it is easier to see what's going on. It opens a little faster, and you can kill processes by highlighting the name and pressing F9 instead of remembering the pid. You can scroll through the process list to see more than the first slew of items. Htop supports mouse operation as well.