Official government source for Scottish genealogy, census and family research - ScotlandsPeople
If you have ancestors from Scotland, you should definitely check out the Scotlands People website at http://www.scotlandspeople.gov.uk/.
The website has almost 50 million records and charges reasonable fees for accessing information. In addition, they have the Scottish census for the years 1861, 1871, 1881, 1891, and 1901. Beyond census records, the site offers birth registers (1855-1905), marriage registers (1855-1930), death registers (1855-1955), parish registers for births and baptisms and marriages and banns (1553-1854), and wills and testaments (1513-1901).