Since freezing compromises the texture, color and even flavor sometimes, I've found that drying works best for me. I rinse the leaves, pat them dry, then place them in a single layer on a baking sheet baking sure there's room around each leaf. I then pop them in the oven at the lowest possible temperature (on mine it think it's 100F). It takes time but leave the basil in the oven until it's completely dry and crisp. I then either keep the leaves whole or crumble them and store them in tightly-sealed jars.
-A balanced diet is a cookie in each hand