I wanted to thank everyone for their suggestions and advice.
I bought a Kobo Glo HD and I'm very pleased with it so far.
The screen is much more responsive than my last eReader (a Sony PRS-650), the light works amazingly well and I'm only using it around a 20% setting.
The touch screen is very responsive, maybe too responsive (as people have commented), but I'm getting used to it.
The support in Calibre, especially with the Kobo Utilities plug-in, is working wonderfully well.
I was a little concerned about the lack of a memory card slot but so far I can fit plenty of books on it, and I have enough technical skills I could try to swap out the SD card if I ever need to.
Chris