SQL ignore part of WHERE if parameter is null

How about something like

SELECT Id, col1, col2, col3, col4 
FROM    myTable 
WHERE   col1 LIKE @Param1+'%'
OR      @Param1 IS NULL

in this specific case you could have also used

SELECT Id, col1, col2, col3, col4 
FROM    myTable 
WHERE   col1 LIKE ISNULL(@Param1,'')+'%'

But in general you can try something like

SELECT Id, col1, col2, col3, col4 
FROM    myTable 
WHERE   (condition1 OR @Param1 IS NULL)
AND     (condition2 OR @Param2 IS NULL)
AND     (condition3 OR @Param3 IS NULL)
...
AND     (conditionN OR @ParamN IS NULL)