The only eReader Barnes and Noble offers presently is the second generation NOOK GlowLight. This version no longer has a slot for a micro SD card. The new version has 4GB of memory but only 500MB is available for non-B&N content. If you have a large collection of non-B&N books, this may be a problem. I have the first generation GlowLight and like it a lot, but one has to be very careful with it. The display has some sort of membrane that disperses the light and is easily damaged. I replaced two of mine under warranty because of this. The new model does not suffer this problem.
I have a large collection of eBooks and use software called Calibre to manage my books. This allows me to store all my books on my computer and I can transfer a few at a time to my NOOK.
Another thing to keep in mind is that B&N is getting out of the tablet and eReader business. I don't know what effect this will have on their sale of eBooks.