I've experimented with this recipe using different alcohols (Irish and Canadian whiskey, rum, brandy and tequila), as well as different syrups (chocolate, cherry, and black currant). The general consensus is that whiskey is the best alcohol, closely followed by rum, and that chocolate is the best syrup. Kaz has also experimented with this recipe, using a cherry vodka he made, and it was absolutely phenomenal.
4 eggs (raw)
14 oz sweetened condensed milk
1/4 cup chocolate syrup
1/4 cup cream of coconut
1 tbs vanilla extract
2 cups Irish whiskey (e.g. Jameson's or Bushmill's - in my opinion, Jameson tastes better)
Blend all ingredients together for 3 minutes. Bottle. Refrigerate for minimum 2 weeks before serving.