Someone just pointed out this interesting climate extremes tool from the Southern Regional Climate Center. Here is the URL: http://extremes.srcc.lsu.edu/
From there you can choose the product, which is the type of all-time record – for the month, for the day, or for the year. Then you select your variable: record high, record low, etc. And finally the month of interest. So far it only does temperatures and is limited to airport data.
Here is a screen shot of the all-time record highs for April in the Midwest. In the tool, instead of this screen shot, when you mouse over one of the records it gives you more details on the record and dates. It is an interesting tool – I just wish it included the longer NWS Cooperative Observer records.