An oldie but still a goodie! My PTO wanted a photo of the library books they funded with our annual book fair. We took a digital photo of each cover, and popped them into a photo collage. Viola! An image that can be shared or used as a screen saver in the media center.
Just put your pictures into a single folder, upload into Picasa (Picasa is a free download). Choose the pictures you'd like in your collage, and click "make collage". You can shuffle the pictures and shuffle the layout. Very nice and very easy!