I guess you've probably already read the news that Google is giving away a trimmed down version of SketchUp. But, in case you haven't:
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Interesting that they're not requiring registration and they're providing an online, searchable 3D model database that you can up/download to/from. There are already a few thousand models up - sure would be handy when you want to pop something into a model or rework one that you found.R