A couple from Louisiana and a couple from the East coast were seated side by side on an airplane. The girl from Louisiana, being friendly and all, said, “So where ya’ll from?” The East coast girl said, “From a place where they know better than to use a preposition at the end of a sentence.” The girl from Louisiana sat quietly for a few moments and then replied: “So, where ya’ll from, bitch?”

An explanation courtesy of the English Chick:
Contrary to popular belief, there is no agreement on this one among English professionals. In general, especially if your audience is strict about rules, don’t end a sentence with a preposition. Prepositions are little words that indicate position and such: with, at, by, from, etc. In general a preposition should come before (”pre”-position) the noun it modifies. So you should change
That's the warrior I must talk to
to
That's the warrior to whom I must talk.
However, if too many “to whom”s and “of which”s are making your writing unnecessarily clumsy, go ahead and end with the preposition, especially in informal writing. Remember the famous example (credited to Winston Churchill) that goes: “This is the kind of thing up with which I will not put!”
Another explanation defense can be found at Mother Tongue Annoyances, a favorite site o’ mine because grammar is where it’s at, bitches.

That’s a variation on my favorite English Teacher joke.
A new guy’s on the campus at Harvard, good and lost. He stops the first student he can find and says “excuse me, can you tell me where the library’s at?”
The student turns up his nose and says “Here at Harvard, we do not end our sentences in prepositions.”
“All right,” our guy responds, “can you tell me where the library’s at, asshole!”
I don’t like ending sentences in “at” (it just sounds too NASCAR to me) but I’m not as opposed to most other forms. Churchill was right - sometimes avoiding an ending preposition sounds worse than leaving it where it is.
You mean: “where you at?” isn’t correct grammar? You sure?
Ah man. I really wanted to hear that YOU were the one who used that on an airplane. I ought to know better than to use the grammar I do. Too easy to be lazy, I suppose.
Hello Grammarians,
I am trying to teach students the difference between prescriptive and descriptive grammar. Students will not accept the fact that a sentence can END with a preposition such as for, from, or which.
Can you help to back this up with a few more examples- students claim Im using adverbs at the end- etc- arguing that “Tell me what the movie is about.” is wrong!
TopTeacher
Palm Springs High School