This is a reasonably priced paid site which is particularly useful for Scottish research.
http://www.genhound.co.uk
This website has historical information on Scotland's counties and parishes taken from the Statistical Accounts of Scotland which were published in the 1790s and 1845. Subscriptions are available but some information can be accessed free of charge.
http://edina.ac.uk/statacc
This site has lots of links to family history resources for Scotland organised into areas such as marriages, censuses, poorhouses etc. There are also some useful county maps showing parish boundaries.
http://www.scotlandsfamily.com/index.htm
This website has details of some marriages and burials for Scotland as well as a comprehensive list of Scottish surname variants.
http://www.scotsfind.org/index.htm
Genealogical gateway for Scotland with information for the whole of Scotland as well as pages for each county.
http://www.genuki.org.uk/big/sct
Official website for Scotland with births, marriages and deaths, census records plus parish registers and wills. Recent additions include Roman Catholic records and RC British Army records from the Bishopric of the Forces. Free searching and then pay-per-view for images of documents.
http://www.scotlandspeople.gov.uk