For our English grammar enthusiast.
Mambo Italiano raised a question in another thread I thought I would post it here. 
From Grammarbook.com
Proper use of WHO/WHOM
Rule Use the he/him method to decide which word is correct.
he = who
him = whom
Examples:Who/Whom wrote the letter?
He wrote the letter. Therefore, who is correct.
For who/whom should I vote?
Should I vote for him? Therefore, whom is correct.
We all know who/whom pulled that prank.
This sentence contains two clauses: We all know and who/whom pulled that prank. We are interested in the second clause because it contains the who/whom. He pulled that prank. Therefore, who is correct.
(Are you starting to sound like a hooting owl yet?)
We want to know on who/whom the prank was pulled.
This sentence contains two clauses: We want to know and the prank was pulled on who/whom. Again, we are interested in the second clause because it contains the who/whom. The prank was pulled on him. Therefore, whom is correct.
From Grammarbook.com
Proper use of WHO/WHOM
Rule Use the he/him method to decide which word is correct.
he = who
him = whom
Examples:Who/Whom wrote the letter?
He wrote the letter. Therefore, who is correct.
For who/whom should I vote?
Should I vote for him? Therefore, whom is correct.
We all know who/whom pulled that prank.
This sentence contains two clauses: We all know and who/whom pulled that prank. We are interested in the second clause because it contains the who/whom. He pulled that prank. Therefore, who is correct.
(Are you starting to sound like a hooting owl yet?)
We want to know on who/whom the prank was pulled.
This sentence contains two clauses: We want to know and the prank was pulled on who/whom. Again, we are interested in the second clause because it contains the who/whom. The prank was pulled on him. Therefore, whom is correct.