In American English, the singular would be used. In British English, either can be used. To quote from Longman English Grammar:

Some collective nouns such as audience, class, club, committee, company, ... can be used with singular or plural verbs.

... when we think of them in an impersonal fashion, i.e. as a whole group:
The present GOVERNMENT, WHICH HASN'T been in power long, ...

... when we think of them in a more personal way, i.e. as the individuals that make up the group:
The GOVERNMENT, WHO ARE looking for a quick victory, ...

End of quote

Note that you must be careful to use "who" with the plural verb as you are effectively referring to people rather than an impersonal organisation.

So: The FBI [organisation] is ...
The FBI [officers] are ...

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Note added at 2 hrs (2009-12-22 22:20:51 GMT)
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A note about police - in both language variants, the correct usage is "the police ARE". The singular verb goes with "the police FORCE IS".

To quote again from the above book:
The following collective nouns must be followed by a plural verb; they do not have plural forms: cattle, the clergy, ..., the police, swine, vermin

The example given is "The police have surrounded the building"

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Note added at 12 hrs (2009-12-23 08:43:25 GMT)
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@ John

Towns and countries usually take a singular verb (even plural nouns such as "the Netherlands"!), although there can be exceptions, at least in BE. If Belgium refers to the football team, the Olympic team etc, then it can be plural. The Daily Telegraph can most certainly take a plural verb, as can Shell, Philips etc (check out their websites)

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Note added at 1 day1 hr (2009-12-23 21:08:59 GMT)
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@ John again

Clearly, "X is a company" is the only possibility, "X are a company" would sound odd to anyone, I'm sure.

However, I worked for Shell for many years and know well that the company sometimes referred to itself with a plural verb. Certainly, there are more instances of singular verb, but the plurals are there too.

Shell produce: http://www.shell.com/home/content/aviation/aeroshell/technic...

Shell anounces + Shell are : http://www.shell.co.uk/home/content/gbr/aboutshell/media_cen...

Shell have : http://www.shell.co.uk/home/content/gbr/aboutshell/careers/s...


My reason for quoting Philips was that I noticed the plural form on their site a while back - of course, I can't find it now apart from in the Eco Design part of this page, where it says "Philips are".

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Note added at 1 day1 hr (2009-12-23 21:20:11 GMT)
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Here, the BBC says (or should I say "say";-)) "the FBI are investigating": http://news.bbc.co.uk/2/hi/7978379.stm

Difficult to really tie these things down, in the absence of clear directives from grammars, which are all busy hedging their bets where British English usage is concerned.