Are you trying to plan a bachelorette party, or shower, and need an online site to plan, organize and invite?  Microsoft recently launched Windows Live Events, a free service with the features you need:

Invite guests, add events directly to your preferred calendar software, or share post-party photos and blogs at Windows Live Events, Microsoft's foray into the online event planning field. In addition to standard online invitation features seen at Evite and other spots, Live Events allows the anticipated weather for an event to be displayed, along with pictures and maps chosen by the host. Live Events requires a Windows Live sign-up to use and can pull contacts from Hotmail accounts, but allows syncing through iCal, Google, and Yahoo calendars, along with Outlook.

This is certainly not an acceptable way to invite your guests to your wedding, but may fit the bill for organizing the less formal aspects of your wedding.

(hat tip: Lifehacker)