Agree w/Martin, but from what you've written (and his first reply is still correct) you can just replace =SUMIF(B2:B5, "John", C2:C5) "John" with the cell reference you have your distinct list - of course one cell at a time.
So if your criteria is in, say cell d2 you point the formula to... =SUMIF(B2:B5, D2 , C2:C5) and just go from there down the list, so it might look like =SUMIF($B$2:$B$1000, D2, $C$2:$C$1000)