My first thought is a cross tabs report, but I haven't used them much in CR.  I have used them more in Reporting Services.  The trick, I think is to a)make sure that there is an entry for EVERY date and b) make all the dates the same format (if they have a time component, strip it off so that the report can group by just the date. (At least this is what is needed in Reporting Services).  I am sure that if I got something wrong, someone will chime in and correct me.