Crown Store
 

Is there an addon that will alert me when the crowns go on sale? If not, would someone make one? I never remember to look and then am unhappy when I find out I missed out.

I don't think there is any API that tells you when crowns are on sale, so an addon cannot notify you. Maybe get on the official forums more often, or follow their twitter account? I'm sure you can also find some online service that generates mail alerts in response to twitter messages that contain keywords like "crown sale" or something.