The best, sadly (for us) is made by Berthillon in Paris. Their main store on an island in the center of Paris at 31 rue St. Louis-en-l'Ile near Notre Dame Cathedral, seems to always have a line. Once on the island, just follow the crowd and you will find it. This is definitely worth the wait.
If you don't want to stand in line, many cafes also serve Berthillon ice cream. The photo above was taken at Le Petit Cler on Rue Cler, another great street of markets and cafes. If you're enticed to go to Paris to try it, check out David Lebovitz's blog, My Paris. Great guide of places to eat and go.