The Ancestry.com Card Catalog is hidden at the bottom of the Search menu, and it is really important. It is a searchable listing of all the the record collections (32,231 at this time) that Ancestry has available.
The reason this is so helpful, is that you can do a search, like Title=Berlin and Keyword=Germany which then gives you back all 15 of the collections you should look at a bit more closely.
Further more, you can filter that by "Birth, Marriage & Death" and suddenly you have found those famous Berlin collections you always have trouble locating!
Here is a great video from Crista Cowan, the Barefoot Genealogist: