I love boiled shrimp but I'm not a fan of cocktail sauce.  I don't think properly boiled and spiced shrimp need cocktail sauce but I know many people won't eat shrimp without it.  Most cocktail sauce is either store bought or just horseradish and ketchup.  You can do so much better.  

½ cup	Heinz chili sauce
½ cup	ketchup
3 tbl	prepared horseradish
1 tbl	lemon juice
1 tsp	Worcestershire sauce ( I like Tabasco Worcestershire sauce)
½ tsp	Vietnamese fish sauce (optional)

Put everything in a bowl and mix it together.  The fish sauce adds a nice little tang if you don't have any this cocktail sauce is delicious without it.