Oh my farking Jesus H Christmas!
aluminIum!
From "A Short History of Nearly Everything," by Bryson:
"The confusion over the aluminum/aluminium spelling arose because of some uncharacteristic indecisiveness on Davy's [Humphry Davy's] part. When he first isolated the element in 1808, he called it 'alumium'. For some reason he thought better of that and changed it to 'aluminum' four years later. Americans dutifully adopted the new term, but many British users disliked 'aluminum', pointing out that it disrupted the '-ium' pattern established by sodium, calcium, and strontium, so they added a vowel and syllable."
So, you see that "aluminum" is the correct form if you go by what it was named by the man himself.