I used 1/4 cup corn syrup and 1/2 tsp Mexican vanilla and it tastes great, but, it does not dissolve in cold drinks.
This was easy, and turned out great! I only used 1/4 cup white syrup, and ended up using probably 1/2 tsp of homemade vanilla. Tasted about like Sonic's Vanilla Coke! ;-) Made for Spring '10 PAC.