Like others, I don't always agree with what they do, but they are "the name" that gets recognized and they do have a lot of lobbying influence. I joined both the NRA and GOA, liked what GOA stands for more than the NRA so I decided to become a GOA lifer first, then an NRA lifer.
They both have payment plans for life memberships, GOA at $50/quarter for the $500 total and NRA at $25/quarter for the $750 total. If you renew your yearly with the NRA early they'll cut you a $10 discount and send you a pretty good coupon book for gun stuff.