My stock battery was getting ridiculous, if I get up at 7am and unplug the phone off the charger, the battery will be pretty much dead by 2pm (<20%).
So last week I picked up HLI-S710EXL from Mugen Power. (You need to go search it on their webiste, I can't post link due to newbie status)
I was hesitant at first because the phone could become bulky due to the extra thickness, but now I'm actually holding the phone better as the extra thickness sits right in the centre of my palm, creating a more natural grip.
Battery life is extended significantly, by the time I go to bed around midnight, usually there is still 35% left in the tank.
I know the price is a bit steep, but I think it's well worth the money, especially if you are not about to purchase a new phone in the near future. I'd totally recommend it.