If you have the data in CSV files, it's probably not that large. Consider using Google Fusion Tables ( https://developers.google.com/fusiontables/docs/v1/sql-refer... ) You can set up simple queries by using SQL syntax (it's easy to learn).
After that, you can set up a simple interface by connecting with Google Apps Scripts, which is easy to learn and to create a simple interactive web site with.
Insert the results of the parsing into any popular database.
Google "<my_chosen_database> delete duplicates"
Edit: without knowing the specifics, you might like to look at Elasticsearch (http://www.elasticsearch.org/). That'll give you an HTTP/JSON API into your data, so you might be able to do all the UI work you need client side, e.g. with Backbone.js (http://backbonejs.org/) or similar.
cat input_file.csv | sort | uniq > output_file.csv
You need to talk about the number of entries you have though, to give us an idea of the sort of tools you need.
* DBD::CSV - Treats your CSV file like it was a RDBMS so can use SQL to inspect/change it - https://metacpan.org/module/DBD::CSV
* Parse::CSV - For parsing large CSV files - https://metacpan.org/module/Parse::CSV
* Text::CSV_XS - Fast CSV parser - https://metacpan.org/module/Text::CSV_XS