I came across a scenario, where I had to change the data in all the datatime columns with in a database. I made use of "xtype" column and wanted to share it. The system table which stores this information is systypes.

SELECT xtype, name FROM systypes 
/* output
34 image
35 text
36 uniqueidentifier
48 tinyint
52 smallint
56 int
*/

From 2005 onwards, MS recommends to use the SQL Server system views instead.

select SYSTEM_type_id,name from sys.types