Another favoured perk, extra holiday is an effective way of rewarding long service or loyalty.
It's also valued by working parents. Extra annual leave offered as reward doesn't cost the employer extra money – as long as you don't need to call in a temp or otherwise make good any shortfall in work.
Bear in mind though, that staff tend to work extra hard before going on holiday, and when they return to a bulging in-tray. However, it's very difficult to remove this perk once it's in place, and you need to ensure that staff consult carefully before taking time off – so you're not left in the lurch with staff away at the same time.
Some companies, especially in creative fields, have instigated occasional 'out of office' days or afternoons, whereby staff are told to spend the day doing something interesting or stimulating – shows, tours, galleries.
Typically staff come back motivated, stimulated and productive. Again, this perk has to be used carefully, so that it does not become an expectation.