Emails to guest communications are the best, highest form of praise, but may take a while to get to the right place.
Stopping by Guest Relations is a more immediate form of recognition. The card you can fill out there still goes to a manager and gets noted on a CM's record card.
These are the "official" ways to thank a CM, if they did a great job and you want to make sure they get recognized for it. But there are still small things you can do or hand out on a larger scale that aren't as big of a deal.
I've gotten a few small items and I still treasure all of them, even if it isn't something that goes on my record. Some examples are small cards saying I made a day magical for the so-and-so family (my fav was Jungle Book themed and read, "Thanks for going way beyond the bare necessities!" and had the family's info on the back), a single serving of instant coffee on the 24 hour day, a small Canadian flag pin (from a family on Canada Day), and a grape soda pin ("The Ellie Badge -- The highest honor we can bestow!").
Again, these are not things that are officially "recognized" by leaders or go on my record, but I've kept every single one and they're still tons of fun.