Brain imps - the rare ones. Marine, SF, Swat etc.
Should they have another stat added to them? Something useful but not overpowering. Like the old +5 to int on the SF/Swat. Perhaps the Marine could have +5 con or dex - something to open up alternative set ups - Pistol tanks and so on.
Obviously numbers would need to be checked to make sure that it doesnt overpower certain classes etc and lead to abuse but the idea i think is sound.