Tool to generate large datasets of test data
The best tool (if you can find it) is DataFactory. (Sadly out of print). I've generated absolutely delightful (and quite authentic-looking) datasets from it.

Generatedata.com is... acceptable, but doesn't scale very well.

DataGenerator is something to keep an eye on.

And while DTM Data Generator is clunky and a poor substitute for DataFactory, it exists and is being sold, and I've used it to generate mildly acceptable data.