This is useful when you do a wrong insert and the ID of your nice table gets messed up. I hate it... so of course for when I need to manually correct this (little note for myself).
To get the current last ID of your table, issue this command:
To reset it, to let say 77:
DBCC CHECKIDENT (yourtable, reseed, 77)
See also: RESEED Post in the SQL Authority Blog