how about some time off? finish work early or even suggest coming in late or having a day off? sometimes this can be very kind. I know my past employers have done this for me and i really knew they appriciated me.
We give our child minder a voucher for a restaurant every Christmas, usually ask if there is somewhere in particular they like to eat and then go the restaurant and pay for a voucher that will pay for dinner. and give it to her as a present.