Visual Studio has ability to delete empty lines in replace operation using regular expressions.
1.Click Ctrl-H (quick replace)
2. Tick “Use Regular Expressions”
3. In Find specify ^$\n
4. In Replace box delete everything.
5 Click “Replace All”
All empty lines will be deleted.

Regular expression for empty line consist of

Beginning of line ^
End of line $
Line break \n

Note that normally in Windows an end of line  indicated by 2 characters CRLF – Carriage Return (CR, ASCII 13, \r) Line Feed (LF, ASCII 10, \n).

Addition from  Kenneth at 6/18/2009:
A regex to remove blank lines that are/aren’t *really* blank (i.e. they do/don’t have spaces):   ^:b*$\n

source:

http://geekswithblogs.net/mnf/archive/2008/03/04/remove-empty-lines-in–text-using-visual-studio.aspx