Sudoku: Medium to Hard

I've been obsessed with sudoku for nearly two years. I do the daily one in the newspaper plus MANY books on cheap thin paper. Sometimes my pencil goes through the paper. Chronicle Books has truly come up with winners. Heavy slick paper. The thing I like most is the size which I can hold in one hand. The thickness is like writing on a table. I received the Chronicle sudoku tablets for Christmas, and on Christmas Day I stayed in my nightie til 5:30 pm working 37 intermediate puzzles from one of your four books. These are the best sudoku books I've ever seen!