G.skill ECO Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory

At the time of purchase you could grab a kit of ECOs for only a few bucks more than a 2x2GB generic DDR3-1333 CL9 kit.

 

Needless to say, it was a great buy for the price (at the time).  These kits are great overclockers, and while rated for 1.35V can run between 1.35-1.65V safely.  They can run with lower timings (6-8-6 or 6-7-6 depending on your kit, these come with either Elpida BBSE or high-binned PSC ICs) or much higher speed (as much as DDR3-2133 with higher latencies) stable.  They run great when two sets (4x2GB) are installed.

 

Although RAM prices have changed, the kit hasn't.  It may not necessarily be a good buy anymore, but it's certainly still a good kit

The ECOs are an excellent set of RAM for those who are after low voltage modules. I have two sets of these (4x2GB) in my 2500k rig and I can tell you these and Sandy Bridge are a match made in heaven.

They easily overclock to 2133MHz with relatively good timings whilst at the same time managing to operate under the Intel recommended max voltage for SB memory (1.58v).

With 1.55v my four dimms run at 2133MHz with 9-10-9-27 timings no problem, they are benchmark stable, and 24/7 folding stable.

I would recommend these for any Sandy Bridge systems wanting good overclocking RAM.