I bought a couple of these for my unlit Kobo Mini's a few weeks ago:
http://www.amazon.com/Great-Deal-Rea...rds=book+light
They work real well, slipping between the cover and the reader. I've used booklights for older Kindles and these have better more even light than the ones I've used in the past. But that was a long time ago. Maybe they've all improved by now.
Last week I sold both of my Kobo Mini's to neighbors and threw in the lights and covers. The people using them seem to like these lights also.
Barry