I print my envelopes. Small 4x5 envelopes with Disney Characters on them. I also print "Thank You Mousekeeping" on them. Then I put the money in it that I plan to tip...seal it...punch a hole in it on the corner.
Then I get some tulle, cut it into a 9 inch circle, place some individually wrapped candy in it, tie it up with ribbon and attach it through the hole in the envelope.
Mousekeeping seems to love it.
$$$$ - we usually tip $1 per day per person unless we have special requests or have been super messy (which never happens). We put all of our towels in a stack, place all of our toiletries together, and move all of our stuff to the benches so that Mousekeeping will only have to change the towels and make the beds.