The green tea sample pack at Nothing but Tea might be an idea to findout what you like, 20 odd different greens from Japan, China and beyond.
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Green tea benefits hugely from being fresh. Tends to be best to order them straight from China or Japan.
Dragon Tea House on ebay is pretty good value, maybe a 100g pack of something from here if you don't want to wade through samples.
Long Jing is possbily the most famous of all the teas produced in China, well worth trying:
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Though the real deal long jing is a little dearer: <!-- m --><a class="postlink" href="http://www.postcardteas.com/tea/green/West_Lake_Long_Jing_Green_Tea" onclick="window.open(this.href);return false;">http://www.postcardteas.com/tea/green/W ... _Green_Tea</a><!-- m -->