I joined Phi Beta Kappa and Tau Beta Pi (engineering honor society) because they seemed to stand for something and accomplish something other than just taking money from people with good GPAs.
At my school PBK membership was only offered to people who had distinguished themselves in two separate courses of study, thus furthering the liberal arts ideal. I think there were about 30 inductees my year, in a school with ~4000 undergrads.
For Tau Beta Pi, you got on the list based on GPA, but leadership and character were taken into account. One individual, for example, was denied membership because he'd backed out on an obligation, causing another student (who wasn't a TBP member) some serious difficulty.
I got invitations from Golden Key and a few others, but I figure my GPA stands on its own; I don't need to pay money to be in a good-GPA honor society.