200 grams lime juice
50 grams water
.5 grams agar agar
Briefly boil the water and agar agar together, then whisk into the lime juice. Chill in an ice bath until it lightly gels, then strain through muslin or a wet paper coffee filter.
This method of clarifying lime juice comes from Dave Arnold of the French Culinary Institute. He explains it in much more detail at his site. Using clarified lime juice in mixed drinks allows one to stir instead of shake, resulting in beautifully clear cocktails.