WP TagMan Wordpress Plugin - Rating, Reviews, Demo & Download
Plugin Description
Rather than manually inserting the scary code that Google Tag Manager provides, this plugin does it properly and puts it into the page in the correct WordPress manner, and in the way that GTM expects.
Of course, you’ll still need to put your tags and pixels into the container, via the GTM interface. You can use Tag Assistant(Chrome plugin) to check that everything looks how it should.