my girlfriend expressed interest in one for christmas. i've looked at kindle, nook, and nook color. they all have their pros and cons, so it really comes down to a matter of personal taste.
kindle - e-ink so it has the "real book" look to it. has a qwerty keyboard with real buttons. some folks don't like the touchscreen stuff, so this is ideal for that croud. lightest of the three. i think they advertise a battery life of 1 month on a single charge. not backlit so you have to have a reading lamp or some sort of light at night.
nook - e-ink so it has the "real book" look to it. instead of button keyboard, has a small touch screen strip for keyboard, navigating menues, etc. advertise a battery life of 3 weeks on a single charge. has sd card slot for external storage of ebooks, etc. not backlit.
nook color - pretty close to being more of an ipad than an e-reader. full touch screen, so doesn't have the e-ink look to it, backlit so reading at night is possible without external light. easier to use if you like to highlight/save exerpts. has a full web browser, can listen to pandora, can play games, watch movies, etc. has read to me capability (at least on select books). sd card slot for extra storage of content. the nook color has different modes for daylight, night, etc that can help reduce eye strain from the backlight.
nook and nook color have apps that run on blackberry, ipad, etc also, so that you can read your purchased material on basically any device. color has wifi, but doesn't come in a 3g version. the other two you can get a 3g version. for nook and nook color, you have e-library so that you can access any of your purchased content from any device, anywhere, anytime. can trade/borrow books with friends somehow (haven't looked into that yet so not sure how it works). can go to any barnes and noble and read anything in their library for free for up to an hour a day on your device.
i've looked at some of the other brands of e-readers. they don't get the publicity of the ones above, but some of them are legit too. i think sony has one that tries to marry touchscreen with the e-ink/monochromatic look.
best buy has nook, nook color, kindle and at least three or four others out on display to where you can play around with them and really check them out.