There's a lot of polymer AR-15-style magazines out there, and for good reason. They're light, durable, practically impervious to the elements and relatively inexpensive. If you consider a magazine to be a "wear item," you want it to work and work well until it doesn't work any more, then replace it.
Some folks prefer metal magazines, for a variety of reasons. Perhaps it's traditional—you feel AR mags have always been made out of metal, so stick with what works. Maybe it's cost—existing designs have been in use for decades, so economy of scale kicks in. Or, perhaps, you've got plenty left over from the '90s when they were hoarded like gold and the only polymer magazines were, well, less-than-optimal.
What whatever reason, if you like metal AR-15 magazines, the folks at E-Lander have got what you're looking for. The E-Lander Mag is made from heavy-gauge steel, has an anti-tilt follower and reinforced floorplate and comes with a body coating designed to resist rust and corrosion.
MSRP: $18.70. Imported to the US from the Mako Group.