Since I already have to buy jeans with a gun in mind, I always try to find the ones with an appropriately sized "watch" or "change" pocket. You know, the little pocket above the main pocket on the right side? If you shop around, you can find jeans that have a large/deep watch pocket that will easily hold one or two magazines. I can't think of a more low-profile way to carry magazines. With the right jeans, its pretty secure. Just something to think about...Make sure you regularly check the pocket for fuzz-bunnies though.
Since not all of my jeans allow for this or when I am not wearing jeans, I use both Ctac and Blackhawk mag pouches. Both work great... For CCW work, you can't always wear your mag/s at 11 o'clock. So long as you practice with where your mags are placed and you put them anywhere insane, it shouldn't matter "what time" you wear them at... With that being said, I wear the Ctac dual mag pouch at around 9 o'clock. It pretty much dissapeers under a T shirt at that position. I wear the Blackhawk pouches in the same position, one on eiether side of the belt loop. These aren't my favorite because they seem to cant inwards, but with sweatpants its about the best you can hope for. I tried wearing a Blackhawk 3 mag nylon pouch at 6 o'clock, which concealed perfectly but I couldn't get to the mags with any real speed.
What I have now works pretty good but I wouldn't say I have found the perfect way to carry mags...I am still searching.