Check to see if text string is found in a column

Ok great Guru's of the Web....I have another challenge for you.

I have two columns of item numbers like below.  The first column (A) are the current items available.  The second column (B) has everything in my system.  What I am trying to do is discontinue everything in my system that is not in column A  

Column A runs from row 1 to row 654,  column B runs from Row 1 to Row 1863.  So I need a formula to put in column C that will look at the entire range of A1 to A654 and check to see if the item numbers in column B are contained anywhere in column A.  ifnot put an "x" in that row, in Column C if it is in the range of column A put nothing.

Any help would be appreciated!

Toydude

Coulmn A        Column B        Column C

DVH41CFX30

CFX30CFX30             
DMF91CFX30             
CMP80CFX30             
CXL04CFX30             
DNR84N8329                x
DGW56N8329                x
DLB40CFY06
CJT42CFY06
CGH18CFY06
CNG71CFY06
DGW54CFY06
DMF90CFY06
CNG87BDH22
DPB60W2202
CJM12BCN36
CNT39N4811
DNM63N4811
DPJ94BCN36
DPK87BCN36
DPF83BCN36
CNG69BCN36
CNG86BCN36
DPB59BCN36
DGC96N8322