This is from the Chicago Manual of Style, 17th edition:
"The phrasing different from is generally considered preferable to different than {this company is different from that one}, but sometimes the adverbial phrase differently than is all but required {she described the scene differently than he did}. In British English, different to is not uncommon—but it is distinctively British English, whereas different from is standard everywhere." (The bolded words are my emphasis.)
And here is something from GMEU, known also as Garner's Modern English Usage:
"Different than is considered inferior to different from. The problem is that than should follow a comparative adjective (larger than, sooner than, etc.), and different is not comparative—though, to be sure, it is a word of contrast. Than implies a comparison, i.e., a matter of degree; but differences are ordinarily qualitative, not quantitative, and the adjective different is not strictly comparative. Hence writers should generally prefer different from. . . Still, it is indisputable that different than is sometimes idiomatic, and even useful, since different from often cannot be substituted for it—e.g.: 'This designer's fashions are typically quite different for men than for women.'
Also, different than may sometimes usefully begin clauses if attempting to use different from would be so awkward as to require another construction—e.g.:
'Life for Swann, who held out to sign a two-year, $7 million contract in August, is a lot different than it was for him in Lynn.' Steve Conroy, 'Ugly Duckling Becomes Swann,' Boston Herald, 13 Sept. 1996, at 104.
When from nicely fills the slot of than, however, that is the idiom to be preferred—e.g.:
' The spell checker it invokes is completely different than [read different from] that which the others share.' Paul Bonner, 'On Windows,' Computer Shopper, Oct. 1996, at 564."
Garner provided more examples; I just didn't list them all. He says the same as Chicago on different to being common in BrE. He adds that while than following differently is a common usage since the 17th century, if no independent clause immediately follows differently, from works well and is preferable. Here is the example he gives:
"Why should artists be treated any differently than [read differently from] scientists?" Roche Schulfer, "Defending NEA," Chicago Trib., 21 Sept. 1996, at 23.