The Sunday Times Travel section on page 13 (4th March 2012) recommended Magic Blackout Blind. Jonathan Futrell for the Good Gear section says
The Magic Blackout Blind ensures you get a good night's sleep when a hotel's blinds or curtains aren't doing their job. Roll Magic Blackout Blind out like cling film, tear off a sheet and trim to fit. It stick to the glass thanks to static, leaves no marks and peels off easily. It's also reusable.
£36 (save £3 this week, now £33)