I've had great success with the basic Betty Crocker cookbook recipe:
8oz cream cheese, softened
1/2 cup butter, softened
2tsp vanilla
6 cups powdered sugar, sifted
I use Philly cream cheese in the rectangular tub, unsalted Sainsbury's own brand creamy English butter, vanilla extract and whatever icing sugar is the cheapest. Works a treat, and we haven't had to refrigerate either before or after icing the cake - but then again I've never made it in the middle of summer here in the UK, and we've always refrigerated cream cheese-iced cakes in the US!