iPlotz.com is a fascinating online wireframe tool. Simple drag-and-drop tools (in an attractive pencil-sketch style) make it easy for even a non-designer like me to map out a common web interface. This includes, of course, forms that are increasingly in demand.
I’m sure this would be very handy even for a graphic designer, although some may feel it hampers creativity by excessive handholding. Personally, I need that sparkplug kickstart to get going.