The following recipe is from Marimar Torres cookbook "The Spanish Table"..., it's the most authentic Sangria recipe that I know of.
3- 750 ml. bottles of full-bodied red wine
2- large lemons, peel and slice thin. Peel can be spiral cut and added to the Sangria
2- large oranges, peel and slice thin. Peel can be spiral cut and added to the Sangria
2- large peaches (when in season), cut in sections
3- tablespoons of sugar, or to taste
1/2 cup finest-quality Spanish brandy, or to taste
1/2 cup orange liquer, such as Gran Torres or Grand Marnier, or to taste
1/4 cup gin, or to taste
Any other fresh fruits such as strawberries and grapes (except melon)
2 or 3 (10-ounce) bottles club soda
Ice cubes
Place all ingredients, except soda and ice cubes, in a large glass bowl or pitcher. Stir well. Taste to adjust ingredients if necessary. Cover and refrigerate for at least 4 hours before serving. At the last minute, add soda and ice cubes, If you make it more than 6 hours before servng, add fruiits like strawberries at the end, so they don't get mushy).