Check out Freshdrop.net. Just click on the Reg Fee tab at the top, then underneath in the next tab area click on the LLLLL or LLLL tab. Over on the right side of the page, you can setup your filters to only show .com or .net or whatever you'd like. I don't think this provides a full list of availables, just shows ones that have dropped within the past 12 days or so, but it's a good place to start.