This is my favorite way to get a party off to a fine start. There is controversy about the origins of this drink - who first mixed it, the exact ingredients, and whether it was a prohibition era invention - if it was it certainly disguises its not insignificant alcohol content well. It tastes just like a grown up soda.

1 oz vodka
1 oz gin
1 oz white tequila
1 oz white rum
1/2 oz Triple Sec
a splash of cola
a dash of lemon juice
Pour ingredients over ice and serve in highball glasses.
2. Pimm's
The origins of this British potion seem more certain - invented by a London oyster bar owner as an aid to digestion in the 19th century. It is a very popular drink at Wimbledon lawn tennis. The following recipe is from the official Pimm's site - anyoneforpimms.com, but I prefer using half lemonade and half ginger ale. I also think adding a little vodka works well.
These measures are per drink, but as above it's probably safest to make a jugful.
50 ml Pimm's No 1
150 ml lemonade
mint, orange, strawberries, cucumber, ice
Pour ingredients over ice and serve in a highball glass.