One of these days, I intend to expand this to a headstamp database. I don't care what the history of any given cartridge is; all I care about is its reloadability and any special concerns with it. That having been said, I would welcome history nuts to add historical notes to this.
I've just discovered a very useful link for headstamp recognition - AFTE.org has a cartridge headstamp gallery!
Headstamps to be Aware Of in All Calibers
AMERC brass: I've been cautioned that "AMERC" brass (especially in 45ACP) should be destroyed on sight, to remove it from circulation. Apparently the primer holes are frequently off center (breaking decap pins), the brass is too soft (tends to bulge when the bullet is seated), and after being fired once, the primer pockets are generally loose enough for the primers to fall out on future reloads. Most reloaders, when encountering "AMERC" stamped brass, crush it with pliers to ensure no one else tries to reload it, then throw it away.
GFL: Fiocchi. Given that the founder was named Giulio Fiocchi, I have a hunch that the Italian word for "ammunition" begins with an L.
*I*: Independence, made by CCI.
WIN NT brass: Plenty of dissenting opinions about this brass. This is Winchester brass using "Non Toxic" primers. Apparently, a lot of folks dislike it because Winchester's putting out small-primer 45ACP brass, instead of the very established large primer tradition. No one particularly loves it, but some folks throw away the brass and others just use small primers to load it. Because Winchester may do the same thing with non-toxic loads in other calibers, this isn't just in the 45ACP reference.
WCC: WCC stands for Western Cartridge Company; it does not mean "Winchester Cartridge Company".
TZZ: TZZ, also encountered as TZ, is Israeli. It's purportedly a clone of WCC brass.