Select first value if exists, otherwise select default value
The shorter query I can think of is

SELECT COALESCE(MAX(Data), 'Default Value')
FROM   Configuration
WHERE  Name = 'NameOfConfiguration';


If the configuration is present it'll take it.
If the configuration is not present the MAX will generate a NULL value (the MAX of nothing is NULL) that will be coalesced to the default value



There is a more generic approach that takes care of what said by Martin Smith in his comment, but is more verbose (using the hypothesis that the configuration name are unique)

WITH Param AS (
  SELECT ID, Data
  FROM   Configuration
  WHERE  Name = 'NameOfConfiguration'
  UNION ALL
  SELECT NULL, 'Default Value'
)
SELECT TOP 1
       Data
FROM   Param
ORDER BY ID DESC


The ID of the Default Value is set to NULL to avoid to use a magic number.
From the BOL: NULL values are treated as the lowest possible values.

IMO a general solution should be used only where a specific one is not possible, and that doesn't seems the case. Also in a generic case the Default Value will need to be a valid value for the datatype of the configuration values otherwise the UNION will return a conversion error.