There's a company that will insure you against having a crappy time at your own wedding. Seriously.
Putting on a wedding is a lot like putting on a show. A very expensive stressful show that's for one night only. There's lots of different vendors, moving parts, and deposits to take care of, and if something goes wrong or, lord forbid, the wedding date needs to be moved, it can be costly, especially considering you have to work on a tight timeline.
Enter Wedsafe, which offers all-inclusive policies that can insure you in the event of cancellations, weather, disaster cakes, and if an overly drunken guest gets into an accident or a fight, in addition to the liability insurance that most venues will require you to purchase.
They're underwritten by the Markel American Insurance Company and have been around since 1999. The liability insurance can be purchased online up to 24 hours in advance of the event and the cancellation insurance can be gotten up to 14 days prior. It's only a few hundred bucks and you can do it all online within a few minutes. Unfortunately, they do not cover losses incurred due to Bridezilla attacks.
I have a better idea. Check your vendors' references, and don't invite people who can't behave. Ta da! No insurance required. Can't help you with the weather though. Don't get married in May if you don't like rain.