Here are a few that I use for my event / party planning:
(they are all FREE)

http://www.seatingarrangement.com/ - For Weddings
http://www.mypunchbowl.com/ - Online Invitations etc
http://www.downloadry.com/most/planning/ (this has a little bit of everything)
http://www.homepartyprofitsoftware.com/login.php - Used this when I did Direct Sales, still a great tool though!
http://www.ezeventplanner.com/ - Event Planning
http://www.ezweddingplanner.com/ - Wedding Planning