DDR4 is on the horizon, but for now if you want fast RAM you'll have to snag something like the Corsair Dominator Platinum CL10 2666MHz kit reviewed at TechPowerUp. eTeknix has the 2133MHz version of this kit on their bench, while HiTechLegion has the 1600MHz mainstream kit from Corsair.
Also at eTeknix is the Crucial Ballistix Tactical DDR3 1866Mhz 8GB kit. This kit is probably one of the most ideal kits of RAM for a "mainstream enthusiast". It's big enough and fast enough to be really useful - but not overkill or overly expensive.