Seido 1750 mAh Battery
So for what it's worth, i had switched to the 1600 mAh battery when it became available and found a marginal improvement over the stock battery. I recently purchased the 1750mAh battery from Seido and this thing rocks. I can actually just let my phone sit idle the entire day with several apps that have push enabled and aside from sending a few texts, a few emails, a few minutes with words and scramble with friends, and a few minutes on Temple Run, the battery will get me through an entire 10 hour work day without the need to charge and when i do finally put it on the charger it's down to about 5% battery left.
I don't know why HTC didn't just launch with a battery of this capacity to begin with.