Glad to hear you're enjoying loose leaf tea. Have you had a look at Adagio's, your hosts, main site. They have a huge selection with most if not all available in samples. Teaspring are also a bet for sampling Chinese teas.
Japanese green tea should be on everyone's list to try, Den's offer a $3 sampler, and I think you can get the $3 off your next order.
Sample, sample, sample would be my advice.
Off the top of my head starter pack would include:
Japan: Sencha, genmai cha.
China: Long jing, tie guan yin, some sort of wuyi oolong, some Yunann black/red tea and keemun/qimen.
India: Darjeeling, Assam
Sencha tends to be bright bold and grassy. Genami cha warming and toasted. Long Jing is perhaps the most subtle of the teas I've mentioned. Tie guan yin often has a wonderful light buttery taste and wuyi tends to be on the other end of the oolong spectrum, dark with more bite. The yunnan blacks/reds are rich and malty, good qimen is to me the pinnacle of black/red tea, classic full body with a tannin bite and some smokey sweetness. Darjeeling also has the tannic bite but ranges from light and floral in the first flushes to dark and full flavoured in the later flush. Assam I find similar to the Yunnan reds, thick and malty.
I don't really do flavoured tea but everyone should at least give some good quality jasmine pearls a shot.