I love the record hints.
For a free genealogy resource website it's quite amazing. It provides access to billions of records not just images but also searchable records that have been indexed. My most used feature is the Record Hints which uses the information I've inputted into my tree and cross checks it with FamilySearch's searchable records data base. This feature has found so many of my ancestors. With 2 records hints I found 8 new ancestors (being Portuguese, the Portuguese parish records do hold lots of information so that helped too). I also use MyHeritage which has a similar feature but I've found the Record Hints on FamilySearch to be more accurate, at least for my family. Plus it's free.
I love that not only does FamilySearch.org give quite accurate record hints, it only gives you access to search through so many records. I am able to help friends this way search for their family anywhere in the world as FamilySearch.org holds so many records worldwide.