American Airporter (415) 546-6689
http://www.americanairporter.com/
Mention yellow page ad for special rates.

SuperShuttle (415) 558-8500
http://www.supershuttle.com/htm/cities/sfo.htm
For trips into SF, wait at any Suppershuttle stop at airport. No reservations necessary. Pick up 2 hours before flight on trips to the airport. Reservations required

BART to SFO or Oakland Airport
http://www.bart.gov/index.asp