Anyways, it's a bunch of numbers... but the extra positive is that the maximums for each month are highlight red. So just search through those quickly, you should find that the maximum 24-hour recorded rainfall in Atlanta history is:
1. 7.36" on March 29, 1886
Second (assuming there was no additional great storm on a different March 29th!) was much more recent:
2. 6.68" on October 4, 1995
You may well be able to dig around the climate category on that Peachtree City National Weather Service page and find more information on the major storms including those, and a better, simpler list. But if not, at least the NowData offers the chance to reliably get answers to many questions like yours.
I know, it's definitely not all the most intuitive. At least it's consistent. And, especially if you have some rudimentary spreadsheet experience, it can be made to tell you what you need rather quickly (in 15 years of meteorology, I still regularly use it myself.) If somebody has a very reliable, comprehensive source for historical data that is fairly straightforward to the typical user, I'd be absolutely right at the front of the line to congratulate them.
(And it is indeed a real pity, that in an era where the big concern is supposed to be changing climate, it still is fairly abstruse and convoluted to get great comprehensive climate information in an intuitive way from an official source)
But hopefully, while it's not absolutely beautiful in method, it not only answered your question, but given you and others the tool to answer the same question and quite a few others on temperature\precipitation climate\history for many other cities around the country!