Most of the time the RAMs voltage does not matter. In fact what you are talking about with the Intel CPUs is the RAM frequency. Most CPUs have a support up to, and most AMD and Intel CPUs support up to 1333MHz DDR2/3.
My mobo has 4GB of DDR2 1066 and is running at 2.1v and is paired with a Q6600 from Intel.
So in your case, 1.8-1.9v RAM will be fine. Just make sure its the right one (DDR2/DDR3) for your mobo.
Wait a minute...back up a moment please.
The JEDEC standard for DDR2 is 1.8V. For DDR3 it is 1.5V. Higher voltages are used by many companies, particularly to achieve stability on timings that are essentially a factory overclock. A component on Intel DDR3 systems (memory controller?) limits voltage to 1.65V, so if your DDR3 RAM needs more, either it cannot be used on an Intel system, or it will run at worse timings at the lower voltage. I would be VERY worried about DDR3 that required 1.8V-1.9; it will generate a lot of heat, and stress your mobo, and likely be unstable at lower voltages. It is inferior RAM, and should be avoided. Get 1.5V-1.6V DDR3, and overclock / tighten the timings yourself.