Leeks are surprisingly easy to preserve. Wash and cut them as if you were about to use them, them place them on a parchment covered cookie sheet in the freezer. Then, once they are frozen (which should take less than 4 hours), place them into a freezer bag. When you get the urge to use them, prepare them as you normally would. In my experience, thawing them is not necessary. They will keep for months, as long as they are kept in a well sealed freezer bag.
I also find them good in dips after a good saute. I replace 1/2 the onions in my french onion dip with leeks or shallots to 'mild' the flavor from the strength of the onions.
I know that if you goto FoodNetwork.com and type in leek you will get a ton of great recipes that call for leeks other then just soup! Have fun with it! (I only go one leek to mature this year. Boooo )