The Well of Lost Plots
Having started with Something Rotten and been largely confused (partly because I didn't know the plot of Hamlet), I've caught up with myself as far as Jasper Fforde's Thursday Next series goes. The Well of Lost Plots is the third in the series and I think the best I've read so far.

A complicated and quite thrilling plot (with very little in the way of those trying-too-hard character names that marred my enjoyment of the first two books), plenty of in-jokes, literary references, and some wonderful ideas and imagery. Unpublished novels where scenery disappears because the author's decided to use it in his new book; a black market in plot devices; slightly steampunk-esque machinery that transmits images to the reader's mind... Trying to write a coherent review of this novel is too hard, partly because it's the third in a series and partly because so much goes on (and not all of it makes sense) so it would be very easy to give things away. As I said to OneMonkey earlier, while I wouldn't rate it quite as highly, I would say that if you enjoy the works of Douglas Adams or Robert Rankin (leaving aside a Dog Called Demolition) this should probably be on your To Read list.