Nvidia and its board partners tend not to be all that great about releasing low profile cards outside of the low end. I think the best low profile Nvidia card you can get right now is the GT 630, which is a rebadged GT 440 from two generations ago. There might be a low profile GT 640 out there, but I've never seen one.
If you need a low profile card now, the best that is commonly available is the low profile version of the Radeon HD 7750. There is even a low profile version of the Radeon HD 7850, but it is extremely rare, produced by only one company called Afox, who I think only sell their products in Europe.
As said above, it's doubtful there will be a 750, Nvidia seems to have ended their little hardware refresh with the 760, and will just be keeping the existing lineup for their lower end.