If you are student, you get a nice student discount for IEEE. Plus, free pizza during the meetings, and opportunities for competitions.
If you aren't a student, I don't really recommend it.
I'm only an IEEE member cause my boss is paying for it, and because its required to join the Robotics & Automation Society (the latter is worth joining, but its an additional $20/year).
I like their IEEE Spectrum magazine, and you get discounts from conferences, but its really not worth the $180+ membership fee . . .