Synchronizing Outlook & Google Apps

Plaxo
http://www.plaxo.com
(web-based)

OggSync
http://oggsync.com

ScheduleWorld
http://www.scheduleworld.com

iCal4OL
http://ical.gutentag.ch

Google Calendar Sync
https://www.google.com/support/calendar/bin/answer.py?answer=89955