Bento Event Planner

"Use the Bento Event Planner to track contacts, vendors, tasks, expenses, location details, important files, emails and more - and link them to any event. It's perfect for planning meetings, conferences, tradeshows, weddings, parties and fundraisers."

The templates are free, but require Bento 3, which sells for $49.00 USD. Of course, you can always try it out for free for 30 days to see if you like it. It does integrate nicely with iOS so you can keep all of your changes sync'd together.