if you notice on the second link i provided, that sony burner can also burn cd-r's as well as the dd discs.
but i feel that once the cds get to large to read in normal cd drives and burners, then they are no longer cds. If you want to be real specific about it, then the red book and orange books define exactly how a cd audio or data should be.
If you are wanting to know the largest capacity of floppy disks compatible with standard floppy drives then 1.44mb is the larges for floppy.
If you are wanting removable storage comparable to floppy disk and superdisk, then there is a vast variety of different formats you can choose from.
Jut to name a few:
Zip disk, both sizes
Jazz discs, i think theres just one size of 2gb
here is an article about different formats and should answer most of your questions.
Any more questions, just let us know.
Also note, if you want to obtain copies of the red book and orange book it will cost you. More info on that can be found here