E-Book readers forum: eBook reader for scientific papers?

Hi everyone. I'm looking for a portable device that will allow me to not only read PDF files, but also highlight but also make notes and comments in the PDF file (or converted from thereof) that can be saved back to my PC. Ideally, the comments I would like to make are not just text, but include non-standard characters like those found in equations. It doesn't have to be an ebook reader specifically. Some kind of tablet or other similar device would be fine with me.

My main goal is to find a light-weight and portable device that will allow me to take notes on scientific papers (principally saved in PDF format) so I don't need to keep printing them out and dealing with them. A full tablet PC could work from what I've seen - Acrobat combined with the unit's ability to save notes written on the screen with a stylus. However, those that I have looked at are either too big or expensive (much more so than many ebook readers), so a lighter and cheaper solution would be preferred. Plus battery life is not as long with a PC compared to many ebook or similar devices.

Has anyone else dealt with not just reading but commenting or marking up PDF files or scientific papers? On either a reader or similar device (iPad, tablet PC, other)? Any suggestions about which might do the job? I've looked at the Kindle DX, the Nook, and some of Sony's ebook readers, but have not found any real satisfactory answers specifically about the marking up of PDF files.

Any help and suggestions gratefully accepted, or questions for clarification. Thanks.