My Kindle is one of my most beloved possessions. I think you are going to love it, Jo.
As has already been suggested, check the top 50 paid-for and free charts on the Kindle page for ideas. Also, take a look at the Kindle discussion forum for loads of information, including details of indie authors, whose books are usually pretty inexpensive. Here's a link to it:
http://www.amazon.co.uk/tag/kindle/forum/ref=cm_cd_ecf_sap?_encoding=UTF8&cdForum=Fx3IRFCNF3E5K2W
I've not read, but have heard good things about, the following inexpensive books:
The Hanging Shed by Gordon Ferris
Room by Emma Donaghue
Jo Nesbo's books
Never Let Me Go by Kazuo Ishiguro
War Horse by Michael Morpurgo (we thought the stage adaptation with the life-sized horse puppets was astonishing!)
The Gold Acorn by Catherine Cooper (free)
Then there are always the free classics.
If you haven't already read the Steig Larsson trilogy, I'd recommend those. Took me a little while to get into the first book, but then I loved all 3 of them.
I'm currently reading "The Eagle of the Ninth" by Rosemary Sutcliffe, but my favourite genres are post-apocalyptical and dystopian. (What a cheerful soul I am.)
I haven't suggested any of my more expensive favourites (over £5), but would be happy to if you don't mind splashing a bit more cash.