I actually have the official HTC extended battery. I actually love the way it feels in my hand w/the battery, even if it sticks out.
It is a 2200mAh battery compared to the stock 1500mAh. I notice a huge difference.
I got it direct shipped from Sprint for 49.99 including the back
If you'd like to see what it makes the phone look like, let me know and I will post some pictures.