The last I bought was Thrill Ride mentioned
here. But that was more because they sounded mildly interesting and you can't go wrong at 0.99$
The last I bought because I was really interested in the book(s) is the Magnificent Devices: Books 1-4 Omnibus. The first, Lady of Devices, is free at
Amazon and a good steampunk novel about a young lady of blood interested in the unladylike pursuit of the sciences in Victorian Britain.