Account names have value, similar to how domain names for websites have value. Each time a new account is created, it uses up the account name forever. An account name that has been used once can never be used to create a new account again.
In order to prevent people from grabbing up all the valuable names for free, the blockchain charges a small fee to acquire the name.
The fee is set by the witnesses. Each witness votes on what they think the fee should be. The blockchain then takes the median value across the 21 witnesses in the round (20 top witnesses + one backup) to get the account_creation_fee to use in calculations.
The blockchain uses the fee from the witnesses to determine the cost of accounts.
30 * account_creation_fee in liquid STEEM.1 * account_creation_fee in liquid STEEM + 29 * 5 * account_creation_fee in Steem Power.(The liquid STEEM used becomes SP in the new account. The Steem Power becomes delegated SP.)
Note: After HF20, this math will be changing as described here.
For quite a long time now, the witnesses have had this fee set to 0.1 STEEM.
What this translates into for a new account is:
Historically the goal for the witnesses has been to keep the USD cost of a new non-delegated account in the $3-5 range.
With the current USD price of STEEM, the cost to create a new account has dropped below $3.00. Based on an effort led by 
I am in agreement that the fee should be increased, so I will be updating mine to 0.2 within the next 24 hours.
Account creation services need to pay special attention to this fee. Ideally they should have their services lookup the current account_creation_fee from the blockchain, so their software dynamically updates anytime the fee changes.
If this needs to be done manually, then it is important that they watch what the witnesses are doing so they know if/when they need to adjust.
You can see what each of the witnesses have set their fee to here: https://steemd.com/witnesses.
You can also see the current median value here: https://steemdb.com/ under the "Consensus State" section:
Most of the major account creation services (steemit.com, AnonSteem, BlockTrades, etc.) are already aware of this, but if you know of any smaller account creation services that may not be following this as closely - you should let them know.