I have a bunch of photos and videos in iPhoto and I'd like to find the largest videos particularly to see if I can delete them to make some space. It seems strange that I can't find an option to do this in iPhoto - am I missing something?
No, there is no way to sort on size in iPhoto. From your context I guess you mean filesize. In iPhoto, size means the dimensions on the Photo (length by breadth, measured in pixels) - see the Export dialogue, for instance. iPhoto is all about the images and not the files that contain them, so I'm not surprised. It's a $15 app, you get a lot, but not everything.