First and foremost, I would recommend an excellent introductory book "Computational Linguistics: Models, Resources, Applications", which is available in printed format as well as in free online or downloadable format. Despite some examples leaning toward Spanish language, most contents of general nature and, thus, is universally applicable to any human language and subject domain.
In addition to the above, I'd recommend to review information, scattered across various pages on the website of The Stanford Natural Language Processing Group, which, among other information, also contain references to research papers and relevant open source software, developed at The Stanford NLP Group.
While not focused on computational linguistics per se, I think that book "Introduction to Information Retrieval", available both in a commercial printed format and as free online and downloadable formats, contains some information, relevant to the question. If you are interested in text classification, one of the corresponding sections in the above-mentioned book has an alternative and much more detailed presentation of the topic in an excellent blog post by Sebastian Raschka.
Finally, another interesting and useful resource (but, less introductory) is an open access research journal Computational Linguistics, published by MIT Press. All resources, mentioned above (with the exception of the first one), are shared as examples. They just barely scratch the surface of the field of computational linguistics and do not represent rich diversity of various research streams.