I would guess Bermuda and Mauritius, in order.

(edit) That is the case, although it's rather a joke because these exchanges are ridiculously tiny...

http://www.world-exchanges.org/member-exchanges

Although I suppose they'll grow in importance as this relativistic arbitrage stuff becomes mainstream.

Well, I feel OK for not realizing Mauritius is there, but alas, I am guilty of being grossly wrong on where Bermuda is, and I can't even blame the thing that taught me how the Caribbean is laid out, Sid Meier's Pirates! for the Commodore 64, which does in fact include Bermuda [1]. (Though for obvious reasons I didn't spend much time up there.) Mea culpa.

[1]: http://project64.c64.org/maps/Pirates%20map.jpg

Bermuda and Mauritius? Not sure why there would be exchanges there.

They're centers of offshore financial activity in the West and India, respectively.