For years and years I've been trimming my garden basil, freezing it, and then using the basil all winter in soup, stew, and pasta sauce, and this post has all my tips for successfully freezing basil. [from KalynsKitchen.com]
Freeze Basil "Pluck the whole leaves and set them in a small paper cup, fill with water until the herb is submerged, then freeze. When frozen solid, pop the block of ice with the embedded herbs out of the paper cup and into a ziplock bag. The herbs, once the ice melts will be fresh and ready to use."