best way to get the userID

 What is the best way of getting the userID??
i dont want to do a dblookup everytime i want the userID across different pages and user controls.
 
also it is the userID i am after, not the user name which i know can be retrieved with Page.User.Identity.Name....
any advice on how i should do this. i only want to do one dblookup then access the user id right across the site from there on.

 
thanks 
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