Depends on the platform. Don't bother OCing a Pentium 4 system without OCing the RAM, too. It's actually disadvantageous to overclock a Socket A system without leaving the RAM and FSB at the same speed, which requires faster RAM, provided you don't have an unlocked CPU.
An Athlon 64 system, on the other hand can gain very significant advantages with overclocked memory, but doesn't need to overclock it's RAM to take advantage of overclocking the CPU. It doesn't need to do either to get an advantage from overclocking the video card. If it's an Athlon 64 system in question (which it should be, since you're getting a new system), and money is tight, value RAM is fine. A 1GB dual-pack for ~$90 will be just fine.