From A Dictionary of Modern English Usage, H.W. Fowler:
"It was once a cherished superstition that prepositions must be kept true to their name and placed before the word they govern in spite of the incurable English instinct for putting them late. . . . The fact is that. . . . even now immense pains are sometimes expended in changing spontaneous into artificial English. . . . Those who lay down the universal principle that final prepositions are 'inelegant' are unconsciously trying to deprive the English language of a valuable idiomatic resource, which has been used freely by all our greatest writers except those whose instinct for English idiom has been overpowered by notions of correctness derived from Latin standards. The legitimacy of the prepositional ending in literary English must be uncompromisingly maintained. . . .
In avoiding the forbidden order, unskillful handlers of words often fall into real blunders. . . ."
"the 'preposition' is in fact [often] the adverbial particle of a phrasal verb, [and] no choice is open to us; it cannot be wrested from its partner"
Examples:
This is the axe he murdered her with!
He didn't know what he was getting into.
We are such stuff as dreams are made on.
She refused to come in.
You can split infinitives to greatly improve your sentences, too!