Tactical Tailor Fight Light pouches or BFG Helium Whisper.
I'm not a huge Taco fan (the pouches, not the food, I'm a huuuuuge taco fan). Also, I don't find them to be particularly low profile when nothing is in them, at least the HSGIs have that plastic "spine" which keeps the pouch proud of the surface. I like the secondary retention that the Fight Lights come with (top bungee) because I've had stuff fall out of pouches before, Tacos were some of the worst offenders, no matter how white-knucklingly cinched down they were.
BFGs are great if lowest profile is your number one requirement, they are flat, just plain totally flat when nothing is inserted in them. Downsides are no top retention standard, and unlike Taco-designs, very difficult to add later on as well. Also, more effort required to re-insert the magazines.
~Augee