I thought it was about time to make a complete list of all the different codes G.Skill uses to mark different ICs and their manufacturers. A lot of valuable info is scattered over many different threads, I tried to collect as much info as I could, please feel free to add more numbers or dispute what I wrote!
G.Skill serial numbers always start with the year and week, for example 913 is the 13th week of 2009 while 1240 is the 40th week of 2012. Pretty straightforward.
After that there are four digits which stand for different ICs/manufacturers:
0000 - Review/Test sample (no IC specified)
01xx - Micron
02xx - Hynix
03xx - Samsung
06xx - Elpida
0690 MxH-E Hyper (small chance of BBSE/EBSE)
07xx - Elixir (/Nanya)
08xx - Nanya (sometimes eTT/uTT)
09xx - PSC eTT/uTT
10xx - Powerchip/PSC
11xx - SpecTek (/Micron)
12xx - Qimonda/Aeneon (sometimes eTT/uTT)
13xx - ProMOS?? (possibly blank IC)
Since April 2012 G.Skill is using new numbers:
AB40 - Samsung/Hynix (seems to be both, only used for a short time)
000x - Hynix (only on samples?)
x10x - Nanya eTT/uTT
x15x - ??? eTT/uTT
x20x - Powerchip/PSC (sometimes eTT/uTT)
x30x - Micron
x40x - Hynix
x50x - Samsung
x60x - SpecTek (/Micron)
x80x - Elpida
3800 MxH-E Hyper
The first digit of the new serial numbers and the last two digits of the old serial numbers might indicate the speed bin originally assigned by the IC manufacturer.
These four digits are followed by six more digits which seem to be consecutive numbers assigned to each kit.
This is it for now!
Of course credit for this goes to many people like Tapakah, stunned_guy and many more!
If you need any more info about a specific memory kit, please visit the RAMlist at i4memory.
Edit 02.11.12: I've added some info from OCX, I see Tapakah has updated his thread tonight as well. ^^
Edit 18.11.12: Update for x100 and x600
Edit 20.11.12: Update for 2100, added 0800
Edit 21.11.12: Decided to put 2100 and 2150 into different categories
Edit 08.12.12: Update for 1240 -> Qimonda
Edit 16.12.12: Small corrections
Edit 22.01.13: Added 1340 -> ProMOS, 09xx changed to "no idea"
Edit 09.03.13: Added 3800 -> Elpida MxH-E Hyper
Edit 25.03.13: Added 0940 -> PSC eTT/uTT
Edit 12.04.14: Added 0690 -> EBSE
Edit 31.05.14: Fourth spot changed to variable
Edit 16.09.14: Added 0150 -> Only D9GTR? (1600 7-7-7 @ 1.9V kits)
Edit 06.10.14: Added 3400 -> DDR4 only so far, marked in italic
Edit 17.11.14: Added 3300 -> DDR4 only so far, marked in italic, seen on F4-2400C15Q-16GRB kit