Trying to organise a party but don't think a plain email invitation will quite cut it? MyInvites offers a wide range of designs and automates the process of sending invitations and counting replies.
The number of categories on the sites is impressive, covering everything from nights in for the boys to The Great Depression (really). You can automatically add a map for your location, and send invitations directly from the site. MyInvites is free to use for up to 100 invitations send per day, requires registration. Got your own favourite invitation-generating site? Share it in the comments.