PhilM,
My advise to you is to join the RAeS as a student before you graduate!
As Genghis said the networking opportunities in the Society are pretty good and might even help land you that first job.
Student membership of the society isn't expensive and you can always think about chartership further down the road if you want to.
Also, something i only recently found out (and not something widely publicised) is that as a student you can attend almost any of the RAeS conferences FREE OF CHARGE. You'd have to reimburse your own travel costs if you wanted to go to any of the conferences but the conference fees themselves can be a fair wad. Opportunity to meet some interesting people and get more current on the industry.