Does anybody have a guide that tells what companies sold or made which kind of receiver?  Something like that would be nice for when I'm browsing a gunshow...

I'm sure there's something somewhere, but I can't remember where it is.

Of the current manufcturers, only DPMS makes any cast lowers.  Their forged lowers have an "F" prefix on the serial number.

Instead of trying to memorize a list, just learn to recognise a cast vs. a forged part.  The easiest way to tell is to look at the lettering and logos on the part.  Raised lettering or inset lettering that looks rough generally means a cast part.  If all of the logos lettering, etc. are stamped then you can be pretty sure it's forged.

Or you could just not worry about it.  I've got two cast lowers and three forged and except for the cosmetics of the lettering there's really no difference.

Quoted: Does anybody have a guide that tells what companies sold or made which kind of receiver?  Something like that would be nice for when I'm browsing a gunshow...

Olyarms makes cast and forged, on the olympic arms website they have a page that tells wheather a lower is cast or forged. Also the serial number for cast generally begins with SGW, however some cast has been sent into olyarms to be destroyed and made into forged, so if you see a lower with serial number beginning with SGW ask if its cast or forged.

National Ordnance receivers are cast also...