Official all-class Paly alumni page:

http://www.palyalumni.net/

LinkedIn: (Let me know if this link still works - Not sure who put this together)

(All years)
https://www.linkedin.com/groups/Palo-Alto-High-School-Paly-4512867?home=&gid=4512867&trk=my_groups-tile-grp

Other Paly alumni websites - NOT recognized by Paly official alumni group:

http://www.alumniclass.com/paloalto