There are the databases available within Access - File, New, and click on
the Databases tab. There are the sample databases that ship with Access
(Northwind, Order, Solutions). You can find sample databases at
http://office.microsoft.com/templates/default.aspx
and
http://www.microsoft.com/downloads/search.asp?
If you go to
www.mvps.org/access you will find sample code (but I don't
think any complete databases). On this site you can click on Resources, and
there are numerous links to other sites, many that have samples. Most
samples though are just to demonstrate a single technique, or code, so you
may not find many complete databases.
Another good site (but again mostly samples demonstrating single techniques)
is
http://www.rogersaccesslibrary.com/
Both these sites will give you a chance to click on the Access WebRing which
will take you to countless other Access sites.