CSV files are a common enough format for data that it's a bit strange Google Docs doesn't open it natively. However, you don't have load up Excel just to check out those files. As tech blog Digital Inspiration points out, it's easy to convert CSV files directly in Google Docs to make them readable.
When you try to open a CSV files in Google Docs you'll be greeted by a "No Preview Available" page. From here, click File > Export to Google Spreadsheet. Google Docs will convert the CSV back into a spreadsheet and you'll be able to open it and work on it in no time. If you're using CSV files a lot, you can set this to happen automatically by clicking the Settings Icon > Upload Settings > Convert Uploaded files to Google Docs format. Now it will automatically convert any unsupported file you upload to Google Docs to its native format.
How to Open CSV Files On Google Docs | Digital Inspiration
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Windows/Linux only: Firefox extension OpenXML Viewer opens Microsoft Word 2007 DOCX files directly in your Firefox browser. Granted, Gmail and Google just started converting DOCX files to HTML for easy viewing, but if you don't use Gmail or you stumble onto a lot of DOCX files linked elsewhere, this extension is a winner if all you want is a quick way to view a DOCX file. OpenXML Viewer is a free download, Windows and Linux with Firefox only. Be sure to check the README for instructions on how to enable OpenXML once it's installed.
Stuck with a PDF file and no application that will let you edit it? PDF UNdo Online is easy, free, works on any computer and there's no registration required. Click to browse your computer for an Adobe PDF document, click to convert it into a Microsoft Word document, then click to download the converted file. Now you can edit it to your heart's content in any application that supports Word documents. A perfect complement for PDF Online, which can convert your edited file right back to PDF. Thanks, PauletteDandoo! 
