I am looking for datasets that contain texts as well as notations for sentence boundaries. I plan to use it to assess a sentence segmentation system. I am mostly interested in texts in English at the moment, but curious about other languages as well.
The Pragmatic Segmenter segmentation library contains sentences for the common edge cases in English as well as some other languages. The README also includes links to a lot of research and other segmentation libraries.
You can also access the Brown Corpus from the NLTK Corpora page. That dataset has been used to test segmentation libraries.