I have since allowed my membership to lapse, but the $42 student membership is well worth it. Looks nice on a resume to be associated with a well-known professional organization, and as manly said, the digital library is well worth it. I once had a Psychology of Interpersonal Relationships class and since it was an interdisciplinary women's studies class, there were people from many majors, and we had to give a presentation on how gender and other pesonal differences (like age, disability, etc) occur in our own fields, and ways to bridge the gaps and help the field appeal more universally.
So I was researching human-computer interfaces, and the aspects that appeal to men, and the aspects that appeal to women, and touched on children as well, and did a bit of theorizing on how to make more unisex HCI, as well as kid-friendly HCI.
I couldn't find ANYTHING in any of the science or psych journals I looked in. Whipped out my ACM membership and hit up their library and was greeted with a wealth of information from a variety of SIGs, not just SigCHI.
The A I got in that class was well worth the $42 fee.