If you choose the option "Search the complete images", you have access to the
complete GRO index 1837-1983 - the only problem on the Ancestry site is that it's still a test (beta) version, and some of the indexing isn't perfect. If you're looking for a surname which doesn't show up, try putting in just the first 2 or 3 letters. The records are all there - finding them is occasionally a bit tricky!
Otherwise, the GRO index is available free in County Record Offices and some libraries (in the UK) as well as LDS centres (worldwide) on microfiche.
It is online (with a better index!) at
http://www.1837online.com/Trace2web/, but this is a pay-per-view site.
The Ancestry site also has a copy of the
partial FreeBMD indexes for the same period - this database is regularly updated, and is also available at
http://freebmd.rootsweb.com/cgi/search.pl, where you can also see which dates have been covered so far.
Rambler