The question's title is straightforward ... can you recommend any decent tool for annotating named entities in a collection of domain-specific textual materials, for instance, medical research papers.  I need to have a large training dataset in order to train my Maximum Entropy Sequence Model. However all the tools I checked online are either inaccurate or very difficult to use.

P.S/ the final output classifiers are domain specific, hence, the medical field is only an example, any recommendations of tools in different domain are most appreciated.

Thank you.

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