My Siege of Petersburg web site research leads me to all kinds of interesting places online. Because there were so many New York units at the Siege of Petersburg, one place I end up finding myself back at time after time is the New York State Military Museum and Veterans Research Center web site, specifically the New York Civil War Units NY State Unit History Project page. On this page you can find links to any New York infantry, artillery, or cavalry unit as well as specialist units like engineers.
Each unit page offers a brief set of histories of a specific unit, usually pulled from Frederick Phisterer’s New York in the War of the Rebellion, but that’s not where it shines. The resources offered include unit rosters in PDF format, transcribed newspaper clippings, some dozens of pages long, images of some soldiers, particularly higher ranking men in a regiment, images of flags, and a Further Reading section which provides a great avenue for more in depth research on a regiment. Transcriptions of diary entries and letters also abound. See their page on the 117th New York, which I was using today, for only one example of the wealth of information available for each unit.
If you have ancestors in a New York regiment or battery or are interested in the units of the state for other reasons, I highly recommend you check it out.