Growing up in the US, I was taught to say "math" and the British "maths" sounded very awkward to me until I noticed mathematics had an 's' at the end, and it occurred to me that it could be considered plural. (To any British reading this, we use the full word "mathematics" in a singular sense also.) I suppose from this perspective, algebra is a math, calculus is a math, topology is a math, etc., though it seems to me that a Brit doing only algebra would still say they are doing maths.
From this new perspective, it occurred to me that physics must be plural as well, but I suppose it would be more granulated. The various physical phenomena themselves (comparable to theorems I suppose) would be too "small" to constitute a single subject (comparable to algebra), and various related phenomena would be grouped together into subjects for study and specialization. (Perhaps this is why we both abbreviate it as the plural physics ... er, wait.)
I looked around for other examples of singular vs plural fields of study and couldn't find much. Biology, chemistry, history, etc. all seem to be singular and follow a different naming pattern. One can study art, or study the arts, and an expert in the field might care about the distinction.
So here's what I'm wondering. Are there other good examples of plural fields of study, especially ones that in various nations (Australia, English as used in India(?), ...) are treated differently with respect to singular/plural?
If someone can publish one comprehensive answer, that would be great, but otherwise I'm guessing the localized info will trickle in from many different people, in which case this will probably work better as a community wiki where we can edit all the various information into one good answer.