If you're buying new extinguishers, I'd recommend checking out water mist extinguishers. We use them at work, and I've done the training/demo with them several times. They are extremely effective and cause much less "collateral damage" than powder or traditional water extinguishers. You can even use them on chip pan type fires instead of a fire blanket.
I have no links with the company, apart from being an impressed user!
http://www.fireservice.co.uk/safety/water-mist-extinguishers
Video:
http://www.safelincs.co.uk/video_player.php?vid=49
edit: Duh - fixed video link