Be sure to check out each one before paying the fee.
Societies like Phi Beta Kappa, Phi Kappa Phi and Omicron Delta Kappa are worth joining if you're asked simply because of their high admission standards and significant post grad network. Some of those societies (PKP in particular) offers a number of scholarships, research grants and travel support to members.
Ultimately, joining an honors society is (usually) no more than another line on the CV but if you can land the "insert name here" research grant, it could mean alot more.
That and it doesnt hurt to be rocking a bunch of honor chords on graduation day. 😎