Sentiment Analysis Datasets
There is an Amazon Customer Review dataset which you can read more about here - the data is stored in S3 and freely available for anyone to use.

It contains over 160 million customer reviews (the README suggests 130 million, but more data must have been added since that was written) made available by Amazon - you can access them in either TSV or Parquet format.

There is also a blog post on using this data set in sentiment analysis here, which links to another post giving more technical detail. In summary, the blog looks at how sentiment correlates with the star rating in the reviews over time, across product categories, etc.