My REI membership has been one of the all-time best investments. It's a once/lifetime $15 fee (NOT annual) and the 10% annual dividend (on non-sale merchandise) more then covers sales tax. There is a window of several months each year when you can use that dividend to get an additional 20% off any non-sale item (except canoes and kayaks, as I recall).
And despite what some competitors say, REI's prices are not boosted to compensate for the dividend.
They are known for one of the most outstanding return policies out there - there was an article in the Seattle Times several months ago about a climber returning his 20+ year old down climbing suit that had languished in his garage; and I once heard someone return X-C skiis that were several years old because he'd decided that they were "the wrong length." We try not to abuse that policy, but it is nice to know that it's there if needed.
No, I don't work for REI. Just a very satisfied cuistomer for many years.
BTW, the Seattle flagship store is only 3 levels (if you include the rental department), but it is large and well-organized. The Denver store seems as large, but a rather confusing combination of many small floors.
My only complaint is that they no longer do performance ski rentals, and the last DH rentals I used from them sucked in sucky snow.