Bubblemon displays something that looks like a vial containing water. The water
level indicates how much memory is in use. The color of the liquid indicates 
how much swap space is used (watery blue means none and angry red means all). 
The system CPU load is indicated by bubbles floating up through the liquid; 
lots of bubbles means high CPU load.

WWW: http://www.nongnu.org/bubblemon/