I've written quite a few HTML scrapers (reading an HTML page, and parsing out information contained in it) and the biggest part of these programs are the string manipulation.  I usually break the HTML page up into string arrays and run through the array looking for keywords.  In .NET, you can break strings up using the .Split method of a string object or you can use Regular expressions.  I find regular expressions powerful, but cryptic to write and maintain, so I use the split method more often than not.  Darren Niemke has benchmarked different methods of spliting strings in .NET