Help Needed - Application covering letter

[Zippee]

Morning,

I'm about to apply for a new job which requires me to send a letter of application along with my CV. Whilst this may not sound too difficult I have been employed in the city since I graduated 6 years ago and have only ever used agencies when moving around and so have never had to write an application letter.
Does anyone know of any good websites I can look at to get an idea of format, length and content for this as I have no idea where to start. Should It link to points in my CV or try to outline why I'm applying etc?

[Big Al.]

YHM