I'd rather keep this site pure and focused on NGP and Xperia Play, but its worth mentioning that Sony is planning its own tablet to compete against the iPad, Androids and PlayBooks of this world. The Android 3.0 tablet should hit in the summer and will likely make use of some of the features in Sony's other product.
That would include Qriocity, the music service, PlayStation Suite offering PSone and other games. If it does ship with a Tegra 2 processor then it might even manage PS2 games, although that's probably Tegra 4 territory. What it won't have is the XMB interface which is rapidly falling out of favour as a user experience.
With all these tablets swamping the market, it will have to have something very special to stand out against the iPad 2, we'll see soon.