Photovisi is an image tool that our class has been using to publish some of their most recent work. You have a range of templates to choose from (some are padlocked - pro users only). Simply select and upload your photos and photovisi will automatically generate your collage.
What my class really liked about this particular tool was the options it gave them to manipulate their collage once their photos were loaded. You can easily crop, replace, delete, add text, change background colours etc.
Here is an example their teacher created for a front page on one of their class wiki.