These three have been usage items for many years. All are Standard and have long been so (different to is limited to British English, however), but only different from seems never to meet objections: She is different from her mother in many ways. He feels different from the way he did yesterday. You look different from him. Different than has been much criticized by commentators but is nonetheless Standard at most levels except for some Edited English. Consider She looks different than [she did] yesterday. He’s different than me (some additional purist discomfort may arise here). You look different than he [him]. The problem lies in the assumption that than should be only a subordinating conjunction (requiring the pronouns that follow to be the nominative case subjects of their clauses), and not a preposition (requiring the pronouns that follow to be the objective case objects of the preposition). But Standard English does use than as both preposition and conjunction: She looks different than me is Standard and so is She looks different than I [do]. And with comparative forms of adjectives, than occurs with great frequency: She looks taller [older, better, thinner, etc.] than me [than I do]. Still, best advice for Formal and Oratorical levels: stick with different from. 1


The Columbia Guide to Standard American English. Copyright © 1993 Columbia University Press.
http://www.bartleby.com/68/37/1837.html

"Different from" is the construction that no one will object to.
"Different to" is fairly common informally in the U.K., but rare in
the U.S. "Different than" is sometimes used to avoid the cumbersome
"different from that which", etc. (e.g., "a very different Pamela
than I used to leave all company and pleasure for" -- Samuel
Richardson). Some U.S. speakers use "different than" exclusively.
Some people have insisted on "different from" on the grounds that
"from" is required after "to differ". But Fowler points out that
there are many other adjectives that do not conform to the
construction of their parent verbs (e.g., "accords with", but
"according to"; "derogates from", but "derogatory to").

The Collins Cobuild Bank of English shows choice of preposition
after "different" to be distributed as follows:

"from" "to" "than"
----- ---- ------
U.K. writing 87.6 10.8 1.5
U.K. speech 68.8 27.3 3.9
U.S. writing 92.7 0.3 7.0
U.S. speech 69.3 0.6 30.1

By Mark Israel at http://alt-usage-english.org/excerpts/fxdiffer.html