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For those looking for non-Apple options, I prefer the Google Nexus line. These are Google's flagship Android devices. The picture is of the new Nexus 10 (10 inch tablet to compete with the standard iPad). The Nexus 10 starts at $399 for a 16 GB wifi version. Android tablets will run all the e-reader apps just like iPad. But overall, there are fewer apps in the Android app stores that are designed specifically for tablets. All that means is that some will be stretched a bit and not look quite as good. But a lot depends on what are your must have apps.
There are a lot of other Android tablets on the market as well, including the Asus Transformer (pictured above) that has a keyboard that attaches and makes the tablet into more of a laptop. Samsung and Acer make very nice tablets as well. All will run all the e-reader apps. Personally, I think that Android tablets are very competitive with Apple iPads. But there is the issue of ecosystems to consider. For anyone who is a Mac or iPhone user, they're probably pretty thoroughly integrated into the Apple ecosystem, meaning they have apps and/or iTunes content that they'd like to use on a tablet. In which case, you probably want to stick with iPads. If your gift recipient has an Android phone, it makes a lot of sense to go with an Android tablet either Google's or one of the others so s/he can use already purchased apps on it.
Microsoft recently came out with its entry into the tablet market the Windows RT Surface. It's competitively priced at $499 for a 32 GB wifi. $100 more for the black touch cover. I haven't had a chance to try one out yet but just about all the reviewers love the hardware. And reportedly it's a good implementation of Windows 8 for tablets. It also comes with a tablet edition of Microsoft Office Home and Student 2013. You can order the keyboard separately, either a touch one as shown or one with raised keys. Reportedly this is a necessary accessory if you're planning to actually use the Office apps. The key drawback at this point appears to be lack of apps. There is a Kindle app available, but so far nothing from Nook or OverDrive. Another thing to consider is that Microsoft is due to release the more full featured version of their tablet early in 2013. It will reportedly be significantly more expensive but also more like a desktop PC. It might be worth the wait.