kuro5hin.org: “On Friday, 20th June 2003, the death knell sounds for US patent number 4,558,302. Having benefitted its owner, the Unisys Corporation for 20 years, the contents of the patent are entered into the Public Domain and may be used absolutely freely by anyone.”
Note however that the patent only expires in the USA tomorrow. The popular GD Graphics Library will not include GIF creation capabilities until the patent expires world-wide on July 7th, 2004.