I've already confessed to buying too much at the farmers' market. Not only do I overstock my kitchen with green beans and zucchini, I hoard herbs, the market's most perishable items. I just can't resist freshly-picked, bright green, fragrant basil at $8/lb. What a difference in quality and price from the expensive plastic packages of wilted herbs at the grocery store.
Basil is hard to keep around: it turns black in the refrigerator and goes limp on the counter. It's best to use it the day it's picked. When you've got a boatload of basil, I've found the easiest way to preserve it is to make and freeze pesto. My pesto is always free form, with basil, olive oil, pine nuts, lemon juice, salt, and black pepper in whatever proportions suit my fancy. I just eyeball it and taste as I go.
Pesto discolors in the fridge unless covered with oil. Freezing it helps it keep longer, and requires no extra oil. Using an ice cube tray allows you to freeze pesto in individual serving sizes, so you thaw and use only the amount you need.
After you've made the pesto, line an ice cube tray with plastic wrap (this makes removing the cubes easy, and keeps your tray from smelling like pesto).
Spoon pesto into each compartment. Freeze, then pull up on the plastic wrap to pop out the cubes. Place the pesto cubes in a freezer safe container and use throughout the fall and winter in soups, salad dressing, sandwiches, and pasta. During the recent hot weather, we've been eating pesto tossed with cold pasta and cherry tomatoes. With the pesto on hand, it only takes 10 minutes to throw together.
Enjoy you herbs!