All these companies seem to be saying to themselves "Wow, Apple sold 2M units and their product doesn't even have a camera or a USB port, and can't play Flash. If we make sure our product has those, we'll be rich!"
Meanwhile, these vendors seem totally oblivious to the all the things Apple got exactly right with the iPad (form factor, battery life, consistent touch-optimized UI, integration with the existing iTunes ecosystem, revenue generation features for third-party developers built into the system, ability to draw on existing iPhone/Mac developer pool obsessed with user experience, etc.). The companies doing this are going to end up with buggy, slow, awkward devices that consumers won't touch, and they'll be scratching their head saying "But we have more features! It makes no sense!"
HP is pretty much the only company that seems to have a coherent response to the iPad. It's rather obvious what happened to their Windows 7 based Slate device. They were planning to ship that as their response to Apple, but then someone at HP actually used an iPad, and said, basically "Holy $h!t, we're not going to match this by taking a Windows 7 netbook and ripping the keyboard off". And fortunately for them, WebOS -- which has the potential to be a very credible tablet platform with a bit of reworking -- happened to be for sale.
Disregard any tablet running a desktop OS; they've been on the market for years and nobody wants them. And disregard attempts by companies that know nothing about platform-building to adapt current smartphone versions of Android (or desktop Linux distros) to tablet use. They'll do it badly, and hardly anyone will write apps with such monstrosities in mind.
Watch HP with WebOS. Watch Google, when they get around to doing a real tablet version of Android. Watch Apple (obviously). And watch Microsoft, when it eventually occurs to them that they need to do a tablet version of Windows Phone 7 rather than pushing desktop Windows 7 on tablets.
Everything else will prove to be an irrelevant sideshow.