Braytech.org is fantastic - has lots of stuff, including Checklists. Each item that's unchecked links to lowlidev, with maps. (You could simply use lowlidev, and skip Braytech altogether, but I find a checklist is easier to scan for missing stuff.)

D2 Checklist is the other big one I use - also useful for a ton of stuff, including scannable checklists. (They also link to lowlidev for the actual maps.) Lots of overlap. (You don't need to log in to Braytech for most of the info, if that matters. Also means you can use Braytech to stalk your friends. :) )

light.gg also has a checklist option - check all three for the interface that works best for you. (They're all slightly different.)

They all have a TON of other info - lost of overlap, but each has unique pieces (some of which are pretty cool).