I have used Data Wrangler before (http://vis.stanford.edu/wrangler/app/) and OpenRefine. But typically, if the dataset is not too large, I tend to use Weka. There are many ETL tools our there too (e.g., http://www.talend.com/resource/etl-tool.html) but I've not used them before. Anybody have any good open source ETL tools to recommend?