I have to disagree with UCFgrad93. Tech gifts are awesome if the recipient likes tech stuff... gender really isn't a factor.
My husband bought me a Kindle 3G for Valentine's Day this year. Love it!
Electronics are only a problem when it's secretly something for yourself. As long as you're not planning on "borrowing" the Kindle (and it's something that your wife will actually use), I think it'll be great. Maybe as an added romantic gesture have it preloaded with poetry?