Have you thought about one of those reading devices that allows you read a book without a book? Most allow you to download a book instantly. Say you are researching at a library and realize you really need the census guide you saw at [chose your favorite retailer]. With one of these devices you can get it right now. The device may also read pdf and other formats that you may already own.
Those devices are nice but they are also pricey and are just one more piece of equipment to carry around.
Did you know you can download the app for those devices to your computer, laptop, netbook, iPad, even your smartphone? Did I mention the apps are all free? You could download them ALL to your laptop. Whether you chose one or all you can have the books - and access to more - but save money by using equipment you already have.
What devices you can use them with and what they can do varies as do the procedures and requirements. You can generally share between devices. With Amazon's Kindle, for example, you can read the book on your netbook at the library, make notes, then pick up where you left off - including the notes - at home on your desktop, then on your smartphone later.
Here are links to the three most popular readers.
Barnes and Noble