The only recipes I've seen are with dark (semi-sweet or bittersweet) chocolate. Here is the one I use:
12 oz. dark chocolate (I use semi-sweet chips)
1 2/3 c. heavy whipping cream
Put the chips (or chocolate pieces) in a food processor, and pulse until a uniform, small size. Heat the cream until scalded, and with processor at low speed, slowly add to chocolate.
You can use it while it's thin, or chill it and use it when it's thicker. You can also add a liqueur, about 2 tablespoons, when you add the cream.
You don't have to process your chips.. just pour the hot cream over them and they will melt no problem. I use bar chocolate and I just break them up into smaller pieces and pour the chocolate on them and let sit for 5 minutes and stir.. works everytime.
I do 8oz of chocolate and 1 cup (8oz) of heavy cream. Double it.. half it.. quadruple it.. it all works. 
I will say though that if you chill it.. it will be hard and you won't be able to spread it. Even at some room temps it will be firm (especially if it's cooler where you are). If it sets up too firm to spread.. just warm it up a teeny bit at a time until it's a good consistency. You can use it just like you would buttercream (but it doesn't crust).
Yes, I should have been clear about that. In my neck of the woods (woods? what are woods?), I have to wait many hours before it begins to set up. Because of that, I chill it for two or three hours, and keep checking it until it's spreading consistency. The chilled ganache is great for making truffles, though!
Here is a link 
http://www.abc4.com/mostpopular/story/Dark-Chocolate-Ganache/vzDk3wQ9ikazBVeuUxurJQ.cspx
This is a really good one 
http://www.joyofbaking.com/ganache.html
and here is another one:
http://allrecipes.com/Recipe/Chocolate-Ganache/Detail.aspx
and another one
Dark Chocolate Ganache
Dark Chocolate Ganache
Ingredients:
8oz Dark Chocolate, finely chopped
1 cup Double Cream
2oz Unsalted Butter, whipped
Method:
1. Heat the cream gently in a saucepan, stirring until it comes to the boil
2. Pour over the chopped chocolate and stir gently until the chocolate has melted
3. Add half the butter, stirring gently till melted and do the same with the remaining butter until all the butter is incorporated
4. Use as is or place in the fridge for a more solid ganache
Keeps in the fridge for 2 days and the freezer for up to a month
I hope this can help you
mmmmmmmmm truffles.. *drool* I just started a diet... 
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