On the retail side other than MB, there's IB, PFG Currenex, EFX, and HotSpotFXr (though spreads are not nearly as low as HotSpotFXi).
Of that list, I'm only familiar with IB. I'm with them now, but am considering switching platforms. Probably will end up going with a prime broker & HotSpotFXi, but everything in that space has to be negotiated.
