It is early to speculate, but gossip has been flying around about San Francisco Opera productions beyond the 2008-2009 season that was just announced.
Starting with the press release [PDF], Peter Grimes will be performed in 2009-2010, conducted by Donald Runnicles. He'll also return for the presentation of whole Ring, which I heard will not be done until 2011, because of scheduling conflicts. Nina Stemme shall be singing Sieglinde, and the SF Chronicle says that Torsten Kerl is being considered for Siegfried.
La Fanciulla del West was supposed to be in the 2006-2007 season, but was replaced by Die Fledermaus. The Chronicle reported that Fanciulla is slated for 2009-2010, Salvatore Licitra will sing Dick Johnson/Ramerrez. I heard a rumor that Deborah Voigt will be singing Minnie.
Jake Heggie's Moby-Dick will be at San Francisco Opera some time after its premiere in the Spring of 2010.
Other unsubstantiated possibilities include Il Trovatore with Sondra Radvanovsky, Stephanie Blythe, Dmitri Hvorostovsky, and Marco Berti; Il Trittico with Patricia Racette and Paolo Gavenelli; The Makropoulos Case with Karita Mattila; and Salomé with Nadja Michael.