Which bank/entity offers the highest risk free interest rate ?

No investments are risk free.

Government Bonds, Totally risk free.

Government bonds are certainly low risk, but they are not risk-free. 
There has to be a government there willing to repay them on maturity. 
If the revolution comes, or the national debt has to be repaid and
deposited funds are requisitioned, or a period of hyper-inflation
occur,  they will have little value.  Economies do collapse and
governments do fall.  No country is immune.

Invest in helium, I say.  It is hugely useful, and there is a very
limited supply, and when it is gone, it is GONE.

Perhaps the comments below are made after a very literal reading of
the question. Michel123, in finance, the term "risk-free interest
rate" has a very specific meaning. As alluded to in the other
comments, the risk-free rate is the hypothetical return on a truly
riskless asset. Since there is no such thing as a riskless asset in
reality, US Treasury Bonds are used as a proxy. The current
yield-to-maturity on T-Bonds (of any maturity) are used as the
risk-free rate for their specific maturities.

If you're looking for a "risk-free" investment that you can make, I
would recommend a certificate of deposit (CD) at a bank. These are
insured up to $100K by the FDIC, and you can buy multiple CDs at
different banks to get deposit insurance on all of your deposits above
$100K. www.bankrate.com lists the best CD rates nationwide.

You could also look at buying Treasury bonds, although this exposes
you to interest rate risk (fixed-income securities lose value as
interest rates rise). I would only consider the direct purchase of
T-bonds to be "risk-free" if I was absolutely certain that I would
hold them until maturity, in which case I don't care about price
fluctuations in the interim.