There have to be 50 watermelon punch variations floating all over the internet. I've found a few to help you plan your party. Quite a few recipes use a lot of citrus or berry juices, which can mask the flavor of the wonderful watermelon. Watermelon juice or punch does benefit from having some kind of tart juice with it like lemon, grapefruit, or orange. If your watermelon is old, grainy, or not ripe and sweet enough, you might want to try one of the punch versions that contain large amounts of other fruits.

(One more idea is just make watermelon ade instead of punch:
  I use watermelon juice instead of water when preparing lemonade or limeade. It's great!)

Version 1:  Watermelon Party Punch Fizz

1 watermelon, chilled
2 cans frozen concentrated lemon juice
Crushed ice
1 lg. bottle ginger ale

Remove seeds, mash half of watermelon meat or put it in a blender to puree it. Mix watermelon, lemon juice, ginger ale and crushed ice.

Version 2:  ICY WATERMELON PUNCH     

8 c. watermelon, cubed & seeded
1/3 c. orange juice concentrate
1/3 c. fresh lime juice
1 qt. lemon-lime soda
Cubed watermelon, lime wedges & mint leaves for garnish

Freeze watermelon cubes in shallow pan about 6 hours, or until only partially frozen. (If frozen solid, let stand at room temperature for 30-45 minutes.) Puree watermelon and juices until smooth. Pour mixture into punch bowl and stir in soda or tonic water. Add garnishes. Makes about 3 quarts.

Version 3:  Watermelon Punch

Recipe based upon Paula Deen, 2007

6 cups cubed, seeded watermelon
1 cup water
1/2 cup sugar
12-ounce can frozen lemonade concentrate, thawed
2 cups unsweetened pineapple juice
Crushed ice
Measure out 1 cup of hot water and stir in the 1/2 cup of sugar until dissolved. Put this in the fridge to cool off while you cube and seed your watermelon. Now use your blender to chop and liquify the watermelon cubes. If you don't like thick punch, you can pour and press the watermelon through a seive or mesh strainer at this point (it's a lot of work and my family likes pulpy orange juice anyway, so I skip this step).  With the watermelon puree (or juice if you went to the trouble) in the blender, add the sugar water.  Add the lemonade concentrate and pineapple juice and blend well. This is really good over crushed ice. You can use the frozen melon cube trick too!

Version 4: Watermelon Raspberry Punch

6 cups watermelon juice (see note)
2 cups pineapple juice
1 can (12 ounces) frozen raspberry juice blend
1 small can (6 ounces) frozen orange juice concentrate
1/4 cup lemon juice

To make watermelon juice, process small chunks of watermelon, with seeds removed,
in a blender or food processor until they turn to liquid. Make more than you need for this punch,
freeze the extra in ice-cube trays, and use the watermelon cubes to chill the punch.
Combine all ingredients in a large jar or pitcher and chill.