When I worked in television--a job with the one-two punch of both lousy pay AND terrible hours, the station I worked for established an ad trade with a local women's-only gym so all employees who wanted it, could have a 1/2 price membership (there was another gym for the guys). The took the money right out of our paychecks, and we didn't even have to think about it.
The university where I still work occasionally has tons of perks. There's a faculty/staff dining hall that is swanky, has awesome food and is incredibly cheap. All employees who want can have free tickets to concerts and theatre events on campus--I got eight free tickets to Carolina Chocolate Drops a few years back, tickets that retailed at $20 each. All employees has access to the incredibly nice gym on campus, if you don't mind working out next to super fit 18-year-olds.
I worked at a coffee shop for years where we got all the free coffee and beverages we could consume.
My current job at the library means that I get first crack at some of the hot new items, I don't have to pay late fines and I can totally ignore the usual 25 hold limit (it's pretty sweet).
I have to say, possibly my favorite work perk of all time is the lost and found.
Since I've been in libraries for a long time, I've become numbed to all of the valuable things that people just lose and then never bother to look for. Things like glasses, car keys (how do you get home!?!?), flashdrives, a single mitten--this stuff is not particularly exciting, but every now and then you strike gold.
Recently, I've had a bit of luck with the lost and found at work. Someone dropped a Sephora gift card and then never claimed it. We obviously hang onto things for quite a while, but after a reasonable amount of time has passed, you know no one is coming back for it. I took the gift card, worth $27, and sold it to a friend for $20. Recently people have been leaving a lot of bracelets. There's a Rhode Island company called Alex + Ani, and they make bangle charm bracelets that people go nuts for. Personally, I don't get the appeal, but people pay almost $30 for a single bangle, and then proceed to fill up their arms. Perhaps it is because their arms are so full that people keep losing them in the library because I've gotten four so far. One had a co-worker's initial on it, so she took it, the other three I sold on craigslist for $15 each.
A while back, a friend went through her work's lost and found and uncovered a pile of Dave and Buster's Power Cards. We took them, and had a lovely afternoon playing skee ball.
So perhaps the Lost & Found isn't a traditional work perk, but I have had some seriously good luck over the years. I've also thrown away a lot of crap too, don't get me wrong, but every now and then you find something good. The thrill of the hunt!