This is a free citation manager available at www.mendeley.com. It offers simple web access as well as a downloadable app.
In comparison to Zotero, the tool for importing citation information from the web directly into your citation database is a simple button that you drag to the bookmarks bar (must allow pop-ups, though), instead of a browser add-on. The benefit to this is that you sign on via the Mendeley homepage, import your citations using what amounts to a bookmark, and then can cleanly sign out of the website, keeping your information secure.
To cite the stored references, you have to download the desktop app. You can also download a plug-in that works directly with Word or Open Office. Or you can select all of the items you want to cite (hold down control while clicking to select multiple), then right click and select "copy citation," and then just paste it in where needed.