"It depends on what the meaning of the word 'is' is."
-President Bill Clinton to the Grand Jury, 1998
There are lots of sentences out there that end with is, but the above quote is definitely my favorite. Is it okay to end a sentence with is? Like Clinton says, that all depends on your definition.
The Meaning of Is
For reasons unknown, there seems to be some confusion surrounding the meaning of is. When discussing it's viability at the end of a sentence, many people point to the preposition rule. The rule says that prepositions shouldn't end a sentence, but a) that's already been debunked here; and b) is isn't a preposition.
Is is actually a form of the verb to be (third person singular present, to be exact). To be is one of the most oft-used verbs, but it has so many different forms you may not know when you're using it. Is is one of the them, and by all rules of English it's perfectly acceptable to end sentences with verbs -- and Shakespeare's famous for it (to be or not to be).
Some sentences, in fact, would be lot more cumbersome if you felt like you couldn't use is:
Is that where it is?
How long did you say it is?
I don't know what that is.
There are plenty of occasions when you can re-word a sentence to eliminate the use of the word is at the end, but do so only if it improves readability. Like the preposition rule, fear of ending on is is another one of those strange grammar myths that you just can't believe. Lots of sites say it's an abomination, but that's just silly. Always go by the first rule of good grammar: if it sounds right, it probably is.