How to get difference between two rows for a column field?

SELECT rowInt, Value,
       COALESCE(
       (
       SELECT TOP 1 Value
       FROM myTable mi
       WHERE mi.rowInt > m.rowInt
       ORDER BY
             rowInt
       ), 0) - Value AS diff
FROM  myTable m
ORDER BY
      rowInt

SELECT
   [current].rowInt,
   [current].Value,
   ISNULL([next].Value, 0) - [current].Value
FROM
   sourceTable       AS [current]
LEFT JOIN
   sourceTable       AS [next]
      ON [next].rowInt = (SELECT MIN(rowInt) FROM sourceTable WHERE rowInt > [current].rowInt)

EDIT:

Thinking about it, using a subquery in the select (ala Quassnoi's answer) may be more efficient. I would trial different versions, and look at the execution plans to see which would perform best on the size of data set that you have...

EDIT2:

I still see this garnering votes, though it's unlikely many people still use SQL Server 2005.

If you have access to Windowed Functions such as LEAD(), then use that instead...

SELECT
  RowInt,
  Value,
  LEAD(Value, 1, 0) OVER (ORDER BY RowInt) - Value
FROM
  sourceTable

SQL Server 2012 and up support LAG / LEAD functions to access the previous or subsequent row. SQL Server 2005 does not support this (in SQL2005 you need a join or something else).

A SQL 2012 example on this data

/* Prepare */
select * into #tmp
from
(
    select 2  as rowint,      23 as Value
    union select 3,       45
    union select 17,      10
    union select 9,       0
) x


/* The SQL 2012 query */
select rowInt, Value, LEAD(value) over (order by rowInt) - Value  
from #tmp

LEAD(value) will return the value of the next row in respect to the given order in "over" clause.