Every once in awhile it happens that you clear all the leaves on your ancestry.com tree. It's fulfilling, yet, anticlimactic for genealogists with a thirst to find more.
The thing is... there are SO many leaves waiting on your tree, if only you manage to open your family tree to that person. Here are a few tips I've found to help the hints show up (even if they are mostly just other people's trees).
1) Try viewing your family tree under the "family" view as opposed to the "Pedigree" view - this will show many more people and it does really help to bring up more leaves.
2) Download a genealogy computer program such as Mac Family Tree, Legacy or Family Tree Maker. You can export your tree out of ancestry.com and import it into the program and then begin to view your data in many different ways. My most recent project has been to try and find a related person from every county in the United States. A challenge, yes, but it's gotten me using tools that I hadn't used and has me going to people in my tree that I haven't gone to in awhile, and is causing literally hundreds of new leaves.
The key to doing this, though, is the computer programs. All the ones that I use have a "Places" view which allows you to see all the places that you have documented your ancestors and relatives in. If you want to get super nerdy, you can start to make all the places consistent - i.e. USA vs. United States, Lackawanna County, Pennsylvania vs. Lackawanna, Pennsylvania, or St Louis vs. St. Louis.
Once you have your places consistent and you believe that every single place listed is actually distinct, you can start your checklist of the counties and cities and see how far you can get relatives to go across the state, country, world. In the process, if you have enough people in your tree (like the 6,000 I have in mine) - I PROMISE new leaves will come up!
Right now, I am using the "sources" view on Mac Family Tree to go through all the World War 1 Draft Cards (which only list county and state) to add in the city, which is listed when you open up the document itself. I'm finding lots of new towns to check off!
As far as finding all the cities and towns in counties, the best source I've found is hometownlocator.com - you can copy and paste into excel pretty easily if you are using internet explorer (does not work with firefox) - and you have to use the paste special option (anything other than html will work).