Google data set search - Search engine specifically for public data sets

Newsroom summaries - 1.3 million articles and author written summaries

Microsoft open data - Microsoft research open data sets

Stop words - multilingual collection of stopwords. Very useful for search engine design! :)

Data.Gov - USA Government is slowly opening up many datasets to the public

Google Word2Vec - Words and phrases converted into multidimensional vectors that retain some meaning.

KD Nuggets - About 50 great data resources for download here. Everything from Enron emails to NASDAQ data.

Reddit Datasets - Requests and discussion around various datasets

AWS Public data - Human genome, Google N-grams, etc.

Hacker News - Dataset discussion thread and links

Open Science Data cloud - Some overlap with AWS public data

Quandl - A search engine spanning many datasets, particularly financial and economic

UCI Irvine Machine Learning - repository of many datasets for machine learning

Data NSW - NSW Government data sets (also take requests)

World Bank - Economics, growth, health, pollution and more

Freebase - Community curated database of places and things

Million Song Database - a freely available collection of meta data for 1 million contemporary popular music tracks

Apple itunes data - Apps, music, etc from the Apple store.

NFL play by play - Play by play data for 2002-2013 seasons for download (don't ask!).

Common Crawl - public data of almost 5 billion web pages

Nasa Earth Exchange - earth science data including land temperature, atmospheric information and climate change data

Australian Government Data - more than 3,600 datasets from more than 140 Australian government organisations.

USA EPA - Environmental data sets such as pollution, etc

SMS Spam - Sample SMS spam data

Facial recognition - Data for facial recognition technology

Stanford teaching - Examples for statistical learning

Princeton's wordnet - Lexical dataset for the english language

Stanford Large Network - Great for network analysis like social networks, etc

Google's web corpus annotate with Freebase concepts - Entitisation

Google's public data search - Search for public data sets here

Google's public transit data feeds, e.g. bus and trains

First names CSV - Over 5,000 common first names

Last names CSV - Over 80,000 common last names

World universities - SQL dump of over 16,000 university names, location, web site, etc.

Industry list - Curated list of industries in JSON format

Action words - Words indicating some form of "action" has occurred. Useful for text analysis

Information gain for terms in job advertisements - Using ~600,000 job advertisements, the popularity and information gain of (unordered) trigrams was calculated along with an IDF popularity score. More on Information Gain

Positive and negative user interactions sample - Approx 100,000 learning points from job to resume matching using Sajari. Negative ratios (again for unordered trigrams) generally indicate the IDF score for a term is overvalued in match score calculation.