I freeze them in an ice cube tray, then zip-bag them when they are frozen. When I need egg yolks to make pastry cream, all I have to do is take out the number of "cubes" I need the night before I need them, put them into a bowl, cover with plastic, and refrigerate to thaw.
They also come in handy when making french toast.
Theresa 
Homemade egg noodles! They are really rich when made with egg yolks only, so caution to those on cholesterol diets! Also remember the egg yolk is only about 1/3 of the whole egg, so if you normally use 2 eggs to make a batch of egg noodles, you'll use 5 or 6 to make the same size batch. I used to give bags of frozen egg noodles out in my Christmas baskets to friends. Big hit as no one really makes homemade noodles much anymore.
I mix a little bit of sugar and vanilla then store them in the fridge or freeze them for longer storage. I use them to make sponge cakes. there is a recipe that calls for egg yolks only....I also use them in pastry cream.....French buttercream also uses egg yolks only....
i've got a recipe for a butter sponge cake that takes 6 yolks.
1 c sifted flour
1 tsp baking powder
1/2 c milk
1/4 c butter
6 yolks
1 c sugar
1/2 tsp vanilla
oven 350*
sift dry together. heat milk & butter until butter melts, keep hot. beat egg yolks until thick & lemon colored. gradually add sugar, beating constantly. it'll get almost white. add vanila. add flour mix. stir until just mixed. gently stir in hot milk mix. bake in greased & floured pan for 30-35 mins. don't invert. cool in pan. makes 2 9" rounds.
i actually got this out of a cookbook from about 35 years ago, but no modern versions have it in it anymore. i suppose it's because of the egg yolks. not very "heart healthy" and all that. phooey! when i want cake, i want cake, i wanna be bad not healthy 
anyway, this is a delicious cake & i always make it at the same time i make my angel cake which takes 6 whites. no waste and twice the cake!
Gothgate -
Thanks for sharing that recipe with us. It sounds really easy to make.
Theresa
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