this one from Kester Thompson's Mocktails but with limes instead of lemons. For those wondering, it took 6.5 limes to produce a cup of juice: my wife's exact guess. The result is very satisfying.
There is something about a lime that feels like an extra special treat in comparison to a lemon. Both are lovely but limes have an extra zing. I especially appreciate the tartness of both and limes, with a lower sugar content, have just that little bit more.