The San Francisco Education Fund put together a website called Thank a Teacher Today. On it, you can send a free E-Card to a teacher and say "thanks."
By the way, the April copy of California Educator, the magazine of the California Teachers Association has a mini-poster (see above) reminding us that Wednesday, May 9, 2007 is Day of the Teacher. The theme this year is "Celebrating the Artistry of Teaching." You can also find the poster and other information on their website and at Day of the Teacher 2007.