What can a publisher offer to its best reviewers? As a publisher, every now and then I saw reviews which are so good, I thought I should thank the reviewer with something more than "thanks". What can a publisher offer that will actually be useful?

Ideas:


Cash. This is probably not happening. Cash is too liquid, too precious a resource to offer. The only conceivable way top management might be persuaded is to have a small pool of best reviewer prizes (say 5 prizes/year @ $500 each), company wide. That makes it hard to reward all good reviewers, since there're tens of thousands of reviewers a year. I also suspect that if top management were to entertain such an idea, they'd prefer to have a best paper award.
Best reviewer certificate. I don't see this as very useful though, since it's just a computer graphic. Plus they're easily hacked - I changed one of these to put my name on it instead of the reviewers', which might be enough to deceive a casual observer.
A free book from the publisher's collection. This is more doable but is not cheap (since it also requires postage), so I won't be able to do send many of these - maybe one / year.
Cheaper open access. This is doable: there's a discretionary range with open access article processing charges (to e.g. offer bulk discounts and to waive them for authors from developing countries). However many reviewers never publish in the journal they review for, and even if they do they might not want to publish open access. I am not sure how useful this is.
A personal subscription to ___ journal. Not sure how useful this either since the reviewer probably already has access to the journal via his or her institution, and if not, there are (usually) other ways to access a needed paper.
Something else?


Edit: Thanks for all the answers.


Make best reviewer awards public: this should be easily done. My only concern is that this can break reviewer anonymity for small journals. Still, a central list of all the best reviewers who have reviewed for the publisher should be doable, with the only drawback being someone will have to compare reviewers from different journals (or there'll have to be set numbers of best reviewers for each journal, which would favour small ones at the expense of larger ones).
Give reviewer feedback: unfortunately only the editorial board can do this. The publisher can suggest, but cannot force the editorial board to do it.
Appoint as editors: it's potentially doable, but needs the approval of the rest of the editorial board. 
Free store credit: this is doable, maybe even better than providing free books from the perspective of the publisher. After all, the publisher would not have to pay postage charges, and it's a revenue-generating activity. Making it transferable would be a nice touch!
Free mugs/T-shirts etc: considering publishers make books and journals (instead of mugs and t-shirts), I am not sure this is a good idea.
Reception at conference: the problem with this is the cost. First one would have to rent the necessary space (expensive) followed by send staff there (also expensive). It would be pretty hard to get some kind of personalized welcome; the staff that attend will probably not be those handling the journal for example, and there might be reviewers for multiple different journals at the same reception. I can float the idea, but not hopeful.


Again, thanks for ideas.
There are a number of quite reputable journals that actually do give public "outstanding reviewer" awards, and their value (while not large) is non-trivial.

If the journal announces their awards publicly online, as these tend to do, then there's no worry about faking a certificate or such. It's probably not going to win anybody a job, but it's another line on the "service" or "awards" portion of a person's CV, and it will be noticed in their community.