Here are a few links to websites about the Great Fire of London, and a couple of other places that crop up in The Demon in the Embers:
The Museum of London has a website about the Great Fire which will help you if you have school homework to do on the fire. It even includes an online game you can play to test what you know about the fire.
For a personal account of the Great Fire, there's no better place to look than at the diary of Samuel Pepys. This link takes you straight to the day the fire broke out, but the next few days are interesting too.
In The Demon in the Embers, Joe and his mum visit the Monument, which commemorates the Great Fire of London. It's a very tall column and you can go up it, although Joe decides not to.
At the beginning of the book, Joe is visiting the Tower of London. Although it was built long before Restoration times, it's a great day out. If you can't go though, you can get a flavour of the Tower's history from a video posted on YouTube of the guided tour given by one of the Yeoman Warders. I watched this to make sure I got my facts straight, and loved it!
The Great Fire of London tends to be taught in KS1 now, so the teaching resources available are aimed at children who are generally younger than my readers. If you're a teacher looking for resources (other than mine, which are on the schools page), help is at hand for you on the Save Teachers Sundays website, where you can find Great Fire of London planning and resources, as well as some useful fact sheets on the Museum of London website.