My very very very favorite is Twinings Green Lemon tea. Just plain Twinings Green is okay, but the green lemon is amazing.
One wild thing about it is that it does not become bitter, no matter how long I leave the teabag in the water. Another is that one bag will make about a quart of tea, if you leave the bag in for a while, so I just get it really hot and let it sit for 30-60 minutes. I often start it steeping before going to bed, and drink it the next morning, soon as I get up. (Just blast it a few minutes in the microwave, and I'm good to go.)
A warning though... avoid the Bigelow brand of green lemon tea. I'm by no means a tea snob and will happily drink most any kind of tea offered to me. The Bigelow version is one frantic exception. It's one of the ironies in my life that the tea that's my very favorite has essentially the same name as one of the few that I might risk life and limb to avoid. (It makes me think of warm swamp water...)
As health benefits go, both green and black tea have plenty of clinical data attesting to health benefits, if you drink lots of it. It is much easier to drink lots of green tea as it has very little bitterness, and can be drunk in volume without adding anything to it that might add up to extra pounds 'round the waist. (My dental hygienist spends a little longer cleaning my teeth as a result, but she just says it helps keep her employed, so, no worries...)
Also very interesting is oolong tea, which is sort of a halfway point in the process of converting green tea to black. It's the tea served in a fair number of Chinese restaurants, though some oolongs might have a slightly different flavor.