Reward-Drop ETA: 2016-08-18 21:30:50 UTC (117 weeks, 3 days, 7 hours)
I think this is about as accurate as we can be, this far out.
That assumes 0% hashrate growth between now and block 420,000. That is probably the least likely scenario. The date will depend on what is the average time between blocks which will depend on the average hashrate growth between now and the halving. A hashrate growth of 10% to 20% seems more likely than 0%. That moves the range to March to June 2016.