I just bought the Seido 3500? 3250? mah, not sure which one, but it has a TONNNN of power. Normally when I am at work, I have to bring my charger so that I can charge because it will not last thoughout the day. Right now, I'm at 40% battery, and looking at my Battery Use, that's 1d 0h 38m since unplugged. HUGE UPGRADE for me. I have been using the internet quite a bit, have watched an episode of a tv show, made a few phone calls, have been texting all day yesterday, and have had 3g and sync enabled at all times.
Yes, it will add bulk to the back, but hey, I don't have to carry a charger with me everywhere I go now