13) Doctor Who - The Myth Makers, by Donald Cotton
Once again, Cotton produces a memorable Who novel through a first person narrative: this time he has the poet Homer telling the story of how he witnessed the Doctor and friends interfering with the outcome of the siege of Troy. Homer didn't appear at all in the story as broadcast (though Cotton has him absorb the silent role of the Cyclops played by Tutte Lemkow); constricting the whole narrative to a single viewpoint character does create some difficulties in telling the story, but basically it is a really good story anyway, and while it's not Cotton at the utter peak of his form, it is surely one of the top ten novelisations. Cotton has taken the opportunity to restore as chapter titles some of the punning episode titles scrapped by the production team (eg "Doctor in the Horse").
14) Doctor Who - Mission to the Unknown, by John Peel
This brings together both the single-episode, Doctor-less story Mission to the Unknown, and the first half of the 12-part Daleks' Master Plan, which IMHO is the peak of early Who. It's a dramatic story, centering around the efforts of the Doctor and friends to prevent the evil Mavic Chen from turning over the Solar System to the Daleks. This first section includes much scene-setting on the Dalek base planet, Kembel, and on Mavic Chen's earth; excursions to a couple more hostile planets en route; the tragic deaths of key characters; and ends with the Doctor tricking the Daleks into letting him regain control of the Tardis and escape with Steven and former enemy-turned-ally Sara Kingdom. It's a glorious story and Peel does it justice.
15) Doctor Who - The Mutation of Time, by John Peel
The Daleks' Master Plan is simply too long to constrain inside a single pair of covers (at least at Target length), so Peel wrote it up as two separate novels, though you would be well advised to read Doctor Who - Mission to the Unknown first. Here again we have a grand panorama of Stuff Going On: the Doctor's compatriot, the Meddling Monk, reappears; Mavic Chen passes from hubris to nemesis; the Doctor must accept another death among his closest circle. Peel's treatment of the second half of the story takes slightly more liberties with the version as broadcast, mostly for good reason: the breach of the Fourth Wall at the end of episode 7 is removed, we get a bit more information as to what happens to everyone else after the Doctor leaves, and we get a Steven/Sara spark that will gladden the hearts of Hartnell-era shippers (including the assertion that they spent months together in the Tardis). He does the complex narrative more than justice.
I'd recommend all three of these. Next for me, since I've already read the Dodo novelisations, is Doctor Who - The Smugglers.