Apple sued HTC earlier today for infringing 20 of its patents related to the iPhone. There was some confusion earlier as to the number of patents that Apple had in its lawsuit — turns out Apple filed two lawsuits. One suit was filed with the International Trade Commission, while the other was filed in the District of Delaware. That accounts for all 20 patents. You can see all of the patent descriptions at Gizmodo.
Update: Provided more information on the two lawsuits being filed by Apple.