One thing I noticed wasn't mentioned in those Amazon links was tone sets. As in, does your husband just want to play something that sounds like a piano, or would he like to play around with organ tone sets, string tone sets, etc.? My keyboard (a cheap one, not all that great, so I won't bother saying what it is) has 100 tone sets included. Granted, a lot of them aren't all that nice-sounding, but I love playing around with different sounds.
Now, I may have just missed that detail on the Amazon pages (I didn't look very long), but if your husband might enjoy multiple tone sets, well, it's something to consider.
I'd also second the suggestion to go into a music store. Don't feel pressured to buy on the spot, but definitely ask them as many questions as you can come up with (and have a notepad and pen to take notes!). Around here, music stores love to give you the best (honest) advice they can, simply to make sure anyone who comes through their doors is happy with them, and thus trusts them enough to drop a significant chunk of money if they decide to buy something.