If you're having a hankering for heightening your hashtag education about education (including environmental education), here are 4 heavy-weight, great finds:
FreeTech4Teacher's "7 Ways to Find Teachers on Twitter"
Cybraryman's Educational Hashtag Page
Green Economy Post's "Ultimate Green Twitter Hashtag List: Build Your Online Green Twitter Following"
Letter H pic from http://www.flickr.com/photos/lwr/376717226/ and Twitter Hashtag pic from: http://www.nurelm.com/themanual/2010/10/06/twitter-power-the-twitter-hashtag/