While reading this week's CodeProject newsletter, I came across a well-written article by Tim Mackey called "An intelligent 404 page". It builds on an earlier article by Rui A Rebelo called "More than strcmp(): similarity in strings".
What the two articles have in common is that they both do string comparisons using the Levenshtein Distance Algorithm. The Levenshteing algorithm has been implemented in all sorts of languages, including C# and TSQL.
In the comments for the second article another algorithm, the Ratcliff/Obershelp pattern recognition is mentioned.
All very interesting...