Where can 'DC Comics' be read in e-book form?

Some Doctor Who books are made available for free online reading or downloading at the BBC.

• Human Nature by Paul Cornell
• Nightshade by Mark Gatiss
• Scales of Injustice by Gary Russell
• Empire of Glass by Andy Lane
• The Well-Mannered War by Gareth Roberts
• Lungbarrow by Marc Platt
• The Sands of Time by Justin Richards
• The Dying Days by Lance Parkin

The New Zealand Doctor Who Fan Club has Who Killed Kennedy by David Biship available as a free ebook with the author's permission.
Legally, the only place where you can is the official BBC Doctor Who website. If you go into its classic series archives several Doctor Who novels have been posted online as annotated "e-books". Presumably recent releases from BBC Books are also available for purchase as e-books as well.