iTunes Folder Watch can be especially handy if you're working with a cloud-storage service like Dropbox or Windows Live SkyDrive; any songs you add to those folders from other sources will get automatically added to iTunes.

The free version saddles you with nag screens and a few disabled features, but it gets the job done. You can get a lifetime license for 7.50 Euros, or about $9.40 U.S. That's money well spent, in my humble opinion.

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