I recently gave up on the Nook Color after on-going issues with the non-replaceble battery.  I really like the Amazon Kindle book web site, but was reluctant to purchase another dedicated e-reader.  Since I have both Nook and Kindle books (and a few other e-book companies/formats), the Nexus 7 is the solution that allows me to read pretty much anything.  I have both the Nook and Kindle programs downloaded, but I think I will check out Aldiko that S.Prime mentioned.  Thanks!