While I read primarily on the iPad. The best e-ink B/W ereader imo is the iRiver Story HD. An unknown brand and one that Amazon refuses to sell directly as it stacks up better in some key areas than the Kindle.
I bought it because my wife can't stand reading on the iPad.
The key specs it has over the Kindle is that it runs on Android and has a more powerful processor and higher resolution screen.
It runs at 800mhz and it is an ARM Cortex A8 processor similar to the iPhone 4. It is hands down quicker than any B/W Kindles at page transitions or page flips.
The 6" screen is 1024x768 also the highest resolution at this size in the business. Sharpest e-ink display.
The reason I got it for my wife because it supports more formats than Kindle does. It handles PDF files nicely, supports reflow and does not need conversion.
It also can read zip, CBR, CBZ formats which is huge for people who are into reading comic books, manga, and scanned jpg zipped up.
I didn't want to get the Kindle because it forces you to go to Amazon or read their own format requiring conversions.
The iRiver is tailored for Google books but you can just pop in a SD card full of books or magazines without being locked into these online stores.