Courtesy of Grammar Girl, an easy way to figure out that who vs. whom thing:

Like “whom,” the pronoun “him” ends with “m.” When you’re trying to decide whether to use “who” or “whom,” ask yourself if the answer to the question would be “he” or “him.” That’s the trick: if you can answer the question being asked with “him,” then use “whom,” and it’s easy to remember because they both end with “m.”

I will still never remember, but I can sure try.