Ed Levine just wrote a detailed summary of bagels in New York for the Times:

"...I set out, scarcely a month ago, to eat bagels in all five boroughs and to determine, to the best of my palate's ability, what makes a great and authentic New York bagel. I visited more than 50 establishments. I ate more than three times that number of bagels. In the process, I both horrified practitioners of the carbohydrate-phobic Atkins diet and discovered no less than half a dozen varieties of bagel so good they need no cheese, butter or smoked fish to accompany them.

"Absolute Bagels on the Upper West Side, I salute you! Terrace Bagels, in Windsor Terrace, Brooklyn, huzzah! Cheers to Bagel Oasis, in Fresh Meadows, Queens, and to Murray's Bagels in Chelsea. Hot Bialys in Jamaica, Queens? Bagelry in Murray Hill? They are all superb.

[...]

Levine clearly defines what constitutes a bagel:
"A bagel is a round bread made of simple, elegant ingredients: high-gluten flour, salt, water, yeast and malt. Its dough is boiled, then baked, and the result should be a rich caramel color; it should not be pale and blond. A bagel should weigh four ounces or less and should make a slight cracking sound when you bite into it instead of a whoosh. A bagel should be eaten warm and, ideally, should be no more than four or five hours old when consumed.

"All else is not a bagel.

Via Reenhead.