How do I add a "date since item created" calculated column an existing list?

I am trying to figure out the best way (if there is a way) to add a column to an existing list that will automatically calculate how many days it has been since each item was created. I'd like to create something that is dynamic and will have the number of days change every day... From what I've been looking at, using the "today" trick isn't really a good option?? I'm using SP 2010.

Thanks!