As of today 2017-08, how much monero has been mined out of the total supply? Is there a website where you can check this?
Actually just https://moneroblocks.info/ shows "Emission" in top right corner, so looks like it is about 14.9M
yshurik is correct, current emission is on https://moneroblocks.info/.
In addition, total coins to be issues (eventually!) can be gotten from coinwarz: https://www.coinwarz.com/cryptocurrency/coins/monero (as well as much other useful info).
As of august 2017, total emission is approximately 14.962175 million monero (), increasing at a rate of roughly 4780 (720 times the current block reward of about 6.64 monero) monero a day. https://moneroblocks.info/tx/2b192d6739c31cf973cdec78a715724ef56e3d16090e6d1fd1a58efcdadbb359 is the current top block for reference. This page shows both current emission and block reward.
At any time, you can ask
monerod to calculate the amount of Monero emitted so far. For example, on current testnet (979765 is the current chain height):
print_coinbase_tx_sum 0 979765
Sum of coinbase transactions between block heights [0, 979765) is 13284059.793703353599 consisting of 13281707.066664487079 in emissions, and 2352.727038866520 in fees
This will go through the blockchain and output the total mined Monero found. Note that since this scans all the blocks, it is a slow command.
Here, we see the total emission so far on testnet is 13281707.066664487079 monero. Try it on mainnet!