If you want to replace your Gnome panel with a dock, Avant Window

It appears the Humanity Panel Icons Pack has been updated, and now you can simply run a script to install all the icons (I wasn't awate of this, thanks rkv!).

Tint2 is a lightweight panel/taskbar intentionally made for Openbox3, but should also work with other window managers such as Gnome.

Gnome Color Chooser is a GTK+/GNOME desktop appearance customization tool. It can change the colors for almost anything on your desktop, including the panel colors (font, etc). Unlike applications like Murrine Configurator, this utility does not modify your original themes. This way you can keep sharing your themes without any license or naming conflicts.

I like to keep on top of my machines health.  I like to do this without programs getting in my way, or dedicating desktop space to monitoring applications.  The way I’ve found to do this simply and effectively is with the System Monitor panel Applet.

The suspend/hibernate menu entries in the "System" menu of the Gnome panel are linked to the Gnome Power Manager. If the Gnome Power Manager supports "suspend" or "hibernate", then the corresponding options will show in the menu.

If you do a lot of tweaking to the panels in Gnome or KDE, you've probably run into an instance where you enabled a plugin or changed a setting and need to restart to see the effect (or maybe you locked something up). Instead of logging out or rebooting, we'll just reload the process.

The Gnome Desktop Environment comes with a set of default panel applets included. A little searching in your distribution´s repositories and on the Internet will uncover a few extra applets which are not included in the official Gnome offering, but which you may find very useful all the same. Let's take a brief look at some of them.

SSHMenu is a panel applet for GNOME that allows users to connect to remote computers over SSH with a single click. As Tim explained in his suggestion e-mail:

Ever wonder how you get your panel, tooltips, pop-up and drop down windows transparent? You’ll be enlightened by this thread. I know you can get your panel transparent an easier way, but this doesn’t keep the panel from the theme you are using, and this doesn’t give transparent menu’s, tooltips, …

Inspired by the command wheel in the Neverwinter Nights online game, Kommando is a floating command panel for KDE. Although Kommando's development is almost as slow as an official Debian release, and is only at version 0.5.2, it is already a configurable and convenient addition to the array of panels available in KDE.

Unlike GNOME’s panels and panel applets, KDE 4.0’s plasma widgets don’t have to be placed in a panel. In fact, you don’t need to have a panel at all. Here’s how to remove the bottom panel in KDE 4.0:

1. Browse to ~/.kde4/share/config/ and make a backup copy of of the plasma-appletsrc file. This is the file you will need to edit. You can use the backup to restore the panel and your widgets to their previous configuration.
2.  

Just as easy to add and remove applications or programs icons and descriptions from Windows Start menu, customizing Ubuntu Gnome menu bar panel is a snap for ex-Windows users.

In the current version of GNOME there is no way to turn off tooltips on the panel. This is an annoyance when using the Compiz Fusion Window Previews plugin, which shows a thumbnail of a window. The yellow GNOME tooltip stills shows up under the fancy Compiz preview.