I never know whether to use "toward" or "towards" (is the latter ever correct?). Does anyone know the rule? For example, in a sentence like "send your contributions toward(s) a gift to...," which form of the word would be correct? Thanks for your input!

James J. Kilpatrick, in his book Fine Print, says there is no discernible difference between the two: the British prefer towards; American usage calls for toward. Fowler, however, has a more complicated answer. He notes differences in pronunciation and usage (adjective/preposition). Says use as adjective is obsolete and, as preposition, the -s form is the prevailing one, and the other tends to become literary on the one hand and provincial on the other.

Thank you kindly. That's very interesting and very helpful.

In journalism school, I was told that an "s" at the end of 'toward' is unnecessary according to the Associated Press style book. It is the same for 'backward' and 'forward' -- NKR

I think this is right. In Britain it would be usual to use towards. My Collins (UK edition) lists toward as obsolete, based on the Old English toweard. Instead, it is obviously alive and well and living in the USA.