I wrote an article for the Northamptonshire FHS called Serendipity some time ago – those pleasant chance discoveries we make in family history from time to time.
Does your family tree go back to the 14th century? You might find www.medievalgenealogy.org.uk a surprise as it contains transcripts of tax assessments for Northamptonshire http://www.medievalgenealogy.org.uk/subsidies/index.shtml from 1301 and 1524. What surprised me was that I soon found some of my family names in these records, and many others in parishes that interest me that were still there 600 years later. Sadly a lot to fill in between, but quite an encouragement.