We put it in mashed potatoes - yum!

Oh, also, my friend made a delicious buttermilk panna cotta once....

Last time I had leftover buttermilk, I made oven-baked buttermilk "fried" chicken and it was delicious--just as good as fried, but not greasy. Blend buttermilk, garlic, chipotles in adobo sauce, salt, pepper and marinate overnight. Dredge in flour and breadcrumbs and bake. I used skinless thighs.

I use buttermilk on my oatmeal--it's excellent!

Here's one from Smitten Kitchen. It's good!
http://smittenkitchen.com/2008/07/napa-cabbage-salad-with-buttermilk-dressing/

You could marinate just about any type of meat in buttermilk for a tender result, like buttermilk fried chicken or pork chops marinated in buttermilk. I also think of potatoes when I think buttermilk, like twice baked potatoes mashed with buttermilk, cheese, scallions, whatever you like. You could also do some dredging & frying w/ your buttermilk and make onion rings or fried okra. A beautiful winter greens salad with buttermilk dressing would also be seasonal and delicious. Now I think I'll go buy some buttermilk myself:)

Thanks for all the suggestions - I usually just use up buttermilk in baking, soup, etc. Didn't know you could freeze it. And I agree - the yogurt sub (or just adding a bit of vinegar to milk) avoid the whole issue.

But suddenly I have a hankering for a good salad dressing - and that one sounds perfect, Mrs. Larkin! I don't have any creme fraiche on hand, but I do have sour cream, which I often sub for it when I'm too lazy to go to the store (or too cheap)!

The sorbet sounds great too...oh hell, forget what I said about selling buttermilk in pints!

This recipe for buttermilk almond sorbet from Amanda's NYT cookbook. We love it. I don't bother grinding the nuts with sugar. I just grind some toasted almonds in a mortar and pestle.
http://www.nytimes.com/2007/06/06/dining/064mrex.html

Here's a yummy one: http://www.food52.com/recipes/4889_buttermilk_herb_dressing

I wonder if you can freeze buttermilk? I have the same problem, always a lot leftover. Or the reverse, never have it when I need it, then do the lemon juice in the milk substitution.

also should say that for future reference, you can buy powdered buttermilk and that you can mix up in small quantities.

look for any dressing calling for yogurt, it will be a different consistency but you will be close! also--you could freeze the extra milk if you are stressed about using it. i'm a big advocate of freezing to reduce my single-girl-who-cooks-all-the-time leftovers issues.

According to Harold Magee since buttermilk is cultured it will keep for a long time in the fridge. It. is fine as long as it does not develop pink tinges. If it separates just shake it up to remix. The sell by date does not mean the product should be discarded by the consumer.

Sorry, I don't have a dressing recipe, but next time you need buttermilk, you could always buy yoghurt instead, and let it down with milk - about 2/3rds to 1/3rd milk. Then you have a few more options with the yoghurt.
Another option is buttermilk mashed potatoes.

You could make pancakes or a cake. I usually wind up with extra milk when it's about to expire so I know how you feel.