I've only tried Words with Friends on Facebook and have wondered what the tablet versions are like. Facebook play feels more like play by mail. I'd like something in real time.
I play a fun one called "Letter Bug" but I'm not sure if it's available in the Amazon Appstore. It reminds me of Boggle.
I wrote one called Unolingo but there is only a free version available via sideloading or the Android Market. I'd be happy to provide someone with an .apk if they would be interested in providing feedback.