Ask HN: Best place(s) to find datasets to practice ML and DM?

Anyone know of good websites with collections of datasets that are good for practicing datamining and machine learning?

The netflix prize, www.netflixprize.com is one obvious one, but only 1 set.

Project Gutenberg is another where you can get large amounts of text. http://www.gutenberg.org/wiki/Main_Page

Datasets for medicin would be greatly appreciated.