Updated table with more entries (if it could be edited into my post above, it'd be great!, as I messed up a bunch of photobucket links last week when I did some album reshuffling):
Internal cage floor areas:
Added dimensions in centimeters for European members.
Clarified IKEA Expedit cages: they are now listed in dimensions of "cubes" they take up, e.g. "2 cubes by 1 cube".
Thanks to everyone who helped with measurements of cages I do not own myself.