A request to the readers of this blog: Any good E-book reader ?

Many readers of this blog tell me how nice it is to have filtered and sometimes contextual information on the subject of Compressed Sensing. However, I am getting to the point where, Summer coming, I would like to avoid doing the reading of these articles indoors. Does anybody have some type of experience with any of these E-book readers ?

I have a PDA that reads PDF files but the screen is just not large enough. I could go for a cheap and small laptop, but I am not sure that I want another backpack to move around nor do I feel that the battery would last long enough ( I want that battery to support only the reading not a whole complex Operating system). The point I think I care most are the following:

• Must read adequately a scientific pdf (double column and should have a font for equations)
• Should have more than an hour of battery life.
• Annotation would be nice but is not a primary requirement.
  

I realize that some of these e-readers are slow to turn pages, but as you all have experienced, it's not like we need to do speed reading on articles on Compressed Sensing! Price is important but not that important, i.e. I don't think I want to spend $2000 for one of these very thin slender Macs, but I do not want a $200 readers that does not have enough screen real estate (like the PDA mentioned earlier).

Any ideas or experience you are willing to share ? Thanks in advance.