Ben beat me to it; Design Visionaries has a good line of NX manuals. While not totally comprehensive, they do provide a good foundation for using the software.
"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
Sham Tickoo's book (from CADCIM) beats DesVis book hand's down. Randy Shih has a good one also. All of them are really basic in concept. DesVis title in completely misleading. It most assuredly not an advanced book at all.
I found the design viz books useful but not for a beginner. The content is interesting but it jumps about quite a bit in a confusing way if you are not already quite familiar with the subject matter...