http://www.devarticles.com/c/a/SQL-Server/Extended-Stored-Procedures-Intro-And-10-Cool-Examples/
Authors gives good brief on 10 cool features in SQL Server repository.
xp_fileexist filename [, OUTPUT]
exec master..xp_fileexist 'c:\test.file'
xp_regread root_key, path_key, key_value
master..xp_regread 'HKEY_LOCAL_MACHINE', 'SYSTEM\Setup', 'SystemPartition'
exec master..xp_repl_encrypt @cardNumber1 output
exec master..xp_dirtree 'c:\mydir'
set @xml = ''
exec sp_xml_preparedocument @id output, @xml
select * from OpenXML(@id, '/people/person')
exec master..xp_availablemedia
declare @netname varchar(20)
exec master..xp_getnetname @netname output
print 'The name of my SQL Server is ' + @netname
xp_logevent {error_number, 'message'} [, 'severity']
exec master..xp_terminate_process 3812
exec master..xp_cmdshell @command
echo off
@echo You passed in %1
Now, enter the following code into Query Analyzer and run it:
declare @arg1 varchar(20)
declare @command varchar(50)
set @arg1 = 'Hello'
set @command = 'c:\testbat.bat ' + @arg1
exec master..xp_cmdshell @command