Go to the foot -> Panel -> add to Panel -> Applets -> Utilities -> Tasklist
Another question - I had done the same thing (removed the default panel that was located at the top of the screen when I installed gnome), then added back a panel and had to find and add the tasklist back. However, when I added the tasklist to the new panel, it appeared as four rectangles lined up horizontally. The original tasklist had a nice little 2x2 grid that showed the four desktops. I compared all the settings with that of a fresh install of gnome on another machine, and the tasklist properties are identical. Is there any way to get it to show up as the 2x2 grid instead of the rather largish rectangles?