Working from left to right, I have the date, split into three separate geeklets for formatting purposes. Next to the date is the time, also split for the same reason.
After the first separator bar, I have the current network IP address, which can display IPs for Airport, Ethernet, and iPhone tethering over USB & Bluetooth.
Below that is a Time Machine geeklet which i found on macosxhints that displays the state of my backups and the time since the last backup. It's written in Ruby and the time display is 6 hours off. Up and to the right is a simple Uptime & RAM geeklet.
After the second separator is my currently playing geeklet. It's actually several geeklets combined to look like one. There are two geeklets stacked on each other that display the current track info from iTunes or Spotify, with the iTunes geeklet set to not display anything if Spotify is open. Below that are two track progress bar geeklets, stacked, which display for iTunes and Spotify, depending on which is open. Spotify's has a green indicator, iTunes is blue. Finally, the names of the programs, Spotify & iTunes, are each two geeklets stacked on top of each other, one black, one white. The white one appears when the matching program is open (thus "lighting up" the open program) and disappears when it's closed so that black is displayed again. There's also a volume level geeklet in the center.
Finally the look is tied together using Candybar for the dock and icons, and a program called nocturne to blackout the menubar.