I have noticed on my motherboard which is a Gigabyte GA-M575L1-S4 there is a molex connector on it marked PCIE_12V.
Can anyone tell me what it is used for. My guess is for powering two pci-e cards, is that correct.
Never seen this on a motherboard before.
Your right, usually a graphics card that require more power.
Yeah, that's common for higher powered PCI-e and some AGP cards, but as twdawson said, it's unusual to see it on a motherboard...
Oh, and btw
twdawson, I think you meant to say a GA-M57
SLI-S, not GA-M57
5L1-S (is this the one? [
link]).

Just in case you try search for more details on it. I can't seem to figure out what that connector is for though, and the pictures I found aren't that clear as to whether the M/B has the female or male molex connector.
If it's a female connection on the board, then my best guess would be that a molex to PCI-e power adapter can be connected there instead of on the end of a power cable coming from the PSU... But I've never seen a setup quite like that before, so I'm not sure if that's even done on any boards.
Edit: Ok, I found what it is... It's a male connector on the motherboard, here's a passage from your user manual:
"The motherboard includes a PCIE_12V power connector, which provides extra power to the onboard PCI Express x16 slot. When installing two graphics cards, please connect the power cable from the power supply to this connector." Hopefully that helps clear up what it's for.