After reading the AR-10 and .308 AR FAQs, and doing some poking around, I tried to come up w/ a listing of which magazines fit which .308 AR variant, as well as the other rifles those magazines fit.  As I'm interested in the .308 AR platform, but don't own one, all the following are from the FAQs, manufacturer websites or product reviews on the net, or my imperfect inferrence:

FN FAL metric magazines:
Rock River LAR-8
Bushmaster BAR-10 (discontinued)(inferred)
Armalite AR-10B (modified)
Kel-Tec RFB
FN FAL (and copies)
L1A1 (and copies)

L1A1 magazines:
Rock River LAR-8  
Bushmaster BAR-10 (discontinued)
L1A1 (and copies)
BREN .308

Thermold FAL magazines:
Rock River LAR-8
Bushmaster BAR-10 (discontinued)
FN SCAR-H (modified)(inferred)
L1A1 (and copies)
BREN .308 (inferred)
FN FAL (and copies)
Kel-Tec RFB (inferred)

Moses Mag metric magazines:
Rock River LAR-8 (modified)
Bushmaster BAR-10 (discontinued)(modified)(inferred)
Kel-Tec RFB (modified)
FN FAL (and copies)
L1A1 (and copies)
FN SCAR-H (modified)

Moses LAR-8 magazine:
Rock River LAR-8
Bushmaster BAR-10 (discontinued)(inferred)
FN SCAR-H (modified)(inferred)
L1A1 (and copies)(inferred)
BREN .308 (inferred)
FN FAL (and copies)(modified)(inferred)
Kel-Tec RFB (modified)(inferred)

Rock River LAR-8 magazines:
Rock River LAR-8
Bushmaster BAR-10 (discontinued)(inferred)
FN SCAR-H (modified)(inferred)
L1A1 (and copies)(inferred)
BREN .308 (inferred)
FN FAL (and copies)
Kel-Tec RFB (inferred)

M-14 magazines:
Armalite AR-10B (modified)
M-14
M-1A
Mossberg MVP .308
Ruger Precision Rifle (some issues reported)

Thermold M-14/M-1A magazine:
M-14
M-1A
Mossberg MVP .308(inferred)
Ruger Precision Rifle (inferred)

Armalite Type 1 magazine:
Armalite AR-10B
M-14
M-1A
Mossberg MVP .308(inferred)
Ruger Precision Rifle (inferred)

AR-10B Gen 2 magazines:
Armalite AR-10B
Noveske N6 (discontinued)
Aero Precision (discontinued)

H&K G-3 magazines:
H&K G3/91 (and copies)
Cobb Mfg MCR-200 (discontinued)
Bushmaster MRC (discontinued)
CMMG (discontinued)

Thermold HK-91 magazines:
H&K G3/91 (and copies)
Cobb Mfg MCR-200 (discontinued)(inferred)
Bushmaster MRC (discontinued)(inferred)
CMMG (discontinued)(inferred)

FN SCAR-H magazine:
FN SCAR-H

Moses SCAR magazine:
FN SCAR-H

Thermold SCAR magazine:
FN SCAR-H

Molon Labe Industries magazines:
FN SCAR-H

H&K 417 magazine:
H&K 417

Original Armalite AR-10 waffle mag:
Armalite AR-10
SR-25/DPMS pattern magwells (modified)  https://www.ar15.com/forums/AR-15/Brownells-Retro-Dutch-AR-10-It-s-Official-/123-723047/?page=4#i7607415
HAC-7 (modified)

SR-25/DPMS pattern (also Magpul, et al) magazines:
Armalite AR-10 (original)(discontinued)  (Original Armalite mags will not fit modern guns w/o modification.  Modern mags won't fit original Armalite receivers w/o modification.)
Knight's SR-25
DPMS (Gen 1 & 2)
Bushmaster .308 ORC
Armalite AR-10A
Armalite AR-10B (modified)
Mossberg MVP .308"
Colt LE 901
Handl Defense lower for the FN SCAR-H
Cav Mfg lower for the FN SCAR-H
Ruger Precision Rifle
most other AR .308 platforms on the market

(discontinued) means that model is no longer made.
(modified) means the magazine requires modification to fit that particular rifle
(inferred) means I am inferring the magazine will fit that rifle, based on other information - it's not real world experience or published information
(and copies) means copies or derivatives made by other manufacturers

If there's a magazine type I've missed, or my inferences are incorrect, or I got bad info from somewhere, please post up.  I'll try to add as many links to manufacturer's info & other links as I have time for.  I find it fascinating that Mossberg got their MVP .308 to feed from both M-14 and AR-10 pattern magazines.

19 Aug 2015.  Added the Ruger Precision Rifle, which one upped the Mossberg MVP - the Ruger also feeds from AICS single-stack mags.
9 Sept 2015 - added RRA's LAR-8 mag.  And Molon Labe's SCAR-L mags.
20 July 2020 - added HAC-7

Questions on the Moses SCAR & the BREN .308":

Not seeing the LAR-8 latch on the Moses SCAR.  Anyone have any info?

Does the BREN .308" conversion take metric FAL magazines?

ETA:  Looking @ the Thermold SCAR-H magazine, looks like there's a FAL latch?  Do SCAR-H magazines fit metric FALs?  Can metric FAL mags be modified to fit the SCAR-H?

The Moses SCAR doesn't have the FAL latch.  The LAR-8 will, and presumably can be modified into a SCAR magazine w/ a dremel, the same way plastic Moses & Thermold FAL mags can be modified to fit the SCAR-H.  See revised OP.

Good info, but for the love of god, please stop with the .308", no need for the apostrophe. It's just weird seeing that. Maybe I'm just weird?  

You'd prefer 7.62x51mm?  

Ha! Whatever floats your boat. It's your thread. Good info either way.

Thanks.  Figured out some of my questions above, but these remain:

Will a BREN .308" conversion feed from metric FAL magazines?

Will a Thermold SCAR magazine work in a FAL?

How difficult is it to convert metal FAL mags to work in a SCAR?  Is it possible to convert L1A1 mags?

Anybody have any feedback for the Moses Scar mag yet?

Mine work fine in my limited testing

Will they fit in anything but a SCAR?  ETA:  Updated OP.  Thermold is making M-14 & G-3 mags.  Their M-14 mag would not be suitable for modification to an AR-10B mag, according to Armalite.

Scar 17 only

Ooops.  Got lucky on that mistake.

Updated FAQ w/ new info (to me) about Knight's modifications to original AR-10 waffle mags that gave birth to the SR-25/DPMS pattern:

https://www.ar15.com/forums/AR-15/Brownells-Retro-Dutch-AR-10-It-s-Official-/123-723047/?page=4#i7607415