A preposition is a perfectly acceptable thing to end a sentence with. Seriously. If you find yourself re-writing it as "with which to end a sentence" you're going to come across as stilted and awkward.
It's a useful rule though: an English grammar book that proscribes trailing prepositions is one you needn't spend any more time with. Just put it down and forget that it exists.
Like so many other rules, it results from Latin-steeped scholars of the 19th century who were uncomfortable with the flexibility of their native tongue, and attempted to hem it round. It's understandable. These men knew they could use the full scope of expression of Latin. About the only person who's ever pushed English hard enough to make it creak was James Joyce.
Amusing aside: you can transform transitive verbs into nouns in English directly (to request, a request). You can't similarly transform intransitive verbs because they require a preposition. In German, you would say a for-ask or an of-ask, but we don't accept that in English. Verbs with both forms are an interesting grey area, such as to dig vs to dig for.
It isn't fixed like English, but parts of it are indeed fixed, prepositions being one of them. The issue isn't that putting a preposition at the end of a sentence in Latin gives the preposition undue emphasis, but rather that you simply can't put a preposition at the end of a sentence in Latin[1]. Ending an English sentence with an article would be roughly similar in terms of nonsensicality. As for Joyce, well, you know he's binomeans to be comprendered!
1. It's the same with split infinitives, which you just can't do in Latin short of tmesis (http://en.wikipedia.org/wiki/Tmesis#Latin).
> You can't similarly transform intransitive verbs because they require a preposition. In German, you would say a for-ask or an of-ask, but we don't accept that in English.
i think i'll have a bit of a lie-down now....
Maybe in your lean-to? (Only other example I can think of quickly.)
More seriously, thanks to the grand-parent for squelching the preposition nonsense so soundly.
That means prepositions are very much something you can end a sentence with. And you can start one with a conjunctive too, if it feels right. The rules of grammar are more like the pirate code than an ISO standard - they're more what you might call guidelines, really.
As an example, here's a wonderfully written article by the late statistician, Jacob Cohen: http://www.ics.uci.edu/~sternh/courses/210/cohen94_pval.pdf
-- Winston Churchill, on not ending sentences with prepositions