In defining alternatives to the Xoom, you have to be fair and agree that there are multiple tiers of tablets and at the moment I think the Xoom is in the top tier of android tablets. You can consider one of the many $200 - $300 tablets out there instead of the Xoom, but its not an equal alternative. You would be settling for a lesser tablet.
In the Xoom class of tablets, I think there is the Toshiba and the LG. Maybe the ASUS tablets but I don't know much about them. If size is not important you can add in the new HTC Flyer too maybe and the Samsung.
Tablets like the adam and the Nook are no where in the same category as the Xoom. and in fact, I think they are two or three tiers below the Xoom.
You get what you pay for and the pricing of these tablets does seem to aling to the quality of the tablet.