[Geralt]

Any android 10" tablet, if you want more than ipad.
Samsung Galaxy 10" inch tab is good start. Also Google Nexus, Lenovo Thinkpad Tablet 2, Microsoft surface...etc...etc
There are many options on android market and now on microsoft windows 8 market as well. Do your research.

There really aren't any good eink readers for technical pdf.
Look at it this way, eink readers = fun and play (great for fiction)
Ipad, android tablets = work (great for pdf....providing they are 10")

Bottom line, when it comes to pdf size matters.
Also if annotations is a big thing for you, make sure the tablet you buy has a really good stylus, not just one of those pens ipad has but a real deal.