Scottish Language Dictionaries (SLD) have excellent information on Scots, present and past, in their dictionaries – see their website and the introductions to the Concise Scots Dictionary and the Scottish National Dictionary.

Scots-Online Pittin the mither tongue on the wab!

Scots Grammar including description of the Scots dialects, pronunciation and orthography, Reader, Dictionary and more!

Scots Wikipedia Brief history and description of Scots language in Scots. The site also has other wikipedia articles translated into Scots. English version has different history and outline.