I have been using Family Search for awhile now and wanted to share what I have learned because of the success I have had with searches. This database is provided by the Church of Jesus Christ of Later-Day Saints and is free to use.
It is my understanding that it is still relatively new and can be buggy at times but I have had few problems. I have noticed they are constantly adding new sets of data so it pays to keep checking if you do not find what you are looking for on the first try. They have a wealth of data including census records (not all years though), death records, marriage records, birth records, to name a few. You can browse their home page, Family Search.Org to see what they have and get general genealogy tips and help with searches.
The main search page is located here . It took me a little while to figure out how to refine the results to my needs. Of course maybe because I am terrible in following my own advice, never checked their Help page for searches! At the top of the Results page is a line called Filters. There you have the option of clicking on any number of ways to narrow the results. Some of the filters can be narrowed even further. For example you can filter out everything but the 1900 census results, then filter again for one or more specific states.
I have found this database particularly useful for death records and census data even though I have an Ancestry.com account. I have found records in Family Search that I did not find in other databases. The Early Michigan Death database for 1867 to 1897 is in the Family Search Collection. I have found records for these early deaths in Family Search but not in the original database. I have also found numerous census records in Family Search that I could not find on Ancestry.com. I suspect this is caused mainly by indexing the original data. Old writing is hard to read and different indexers will make different interpretations.
I am firm believer in searching more than one source for records for this very reason. It certainly has benefited my research. Family Search is well worth checking out.