We've practically re-built our village hall on the proceeds of fundraising. We've held all sorts of events, including car boot sales, quiz nights, Burns Nights, St George's Day celebrations, Whist Drives, Coffee Mornings, etc, etc.
Have you tried applying for National Lottery funding? I know of some village halls that have been helped by the National Lottery. Information here:
http://www.lotteryfunding.org.uk/
If you want to apply to businesses for donations, you might find you don't get much support, but in the first instance speak to business people who live in your village. They may be more inclined to help than outsiders would be.
If you are going to write to other businesses, make the letter friendly, short and to the point. Explain briefly what you want to do, and how this will benefit the community as a whole. Don't write a long letter - very few take the trouble to read long letters from people they don't know - especially if they're asking for donations. Don't hold your breath for a positive response from them though. Like us, you may find the only way to do it is by organising fundraising events.
Good luck.