Here is a link – http://www.openspf.org/
SPF configuration with Google’s Postini service – http://www.google.com/support/a/bin/answer.py?hl=en&answer=100354 and http://groups.google.com/group/PostiniSupportForGoogleApps/browse_thread/thread/889c4910261913b4 and http://www.google.com/support/forum/p/AppSecurity/thread?tid=5ecff51e4f36aa69&hl=en&fid=5ecff51e4f36aa6900046180ed6135bc
Microsoft SPF wizard – http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/default.aspx
Misc links – http://www.eggheadcafe.com/software/aspnet/31406053/spf-record-syntax-with-an.aspx