I have had several Nord synths in my time. Nordlead, Nordlead II, MicroModular and Modular Keys.
I recently purchased the Discovery 2.6 that was mentioned above and it's definetely close enough to ther 'real deal'.
It sounds awesome and the import sysex functionality makes it a winner in my eyes.
But download the demo and try it out. Maybe it's not what you're looking for, but IF you're looking for a Nordlead softsynth this is as close as you get.
There is also another synth that people claim sounds like the Nordlead. I DON'T think to but again; it's a matter of taste.
It's called Synth1 and best of all, it's FREE !!
You can find it here: http://www.geocities.jp/daichi1969/softsynth/
For more info in a language you can read go here: http://www.kvraudio.com/get/214.html