Find closest lat long to an input lat long (SQL Server 2008)

What you are looking for is Nearest Neighbor Query. Look at the following links, I think you will find what you are looking for.

Nearest Neighbor Query

Nearest Neighbors

The nearest neighbor optimization in SQL Server Denali

This uses Geography not Geometry (if data is Lat/Lng you data should be Geography Type not Geometry)

"The SQL Server geography data type stores ellipsoidal (round-earth) data, such as GPS latitude and longitude coordinates."

To Select the Top 5 Nearest Records from a lat/lng (-122.0 37.0) point you can use.

SELECT   TOP 5
         geography::STGeomFromText('POINT(-122.0 37.0)', 4326).STDistance(p) 
FROM     markers
WHERE    geography::STGeomFromText('POINT(-122.0 37.0)', 4326).STDistance(p) < 25
ORDER BY geography::STGeomFromText('POINT(-122.0 37.0)', 4326).STDistance(p);