What is the y-intercept for all graphs of the form y=ab^x (where b is not 0)

The y-intercept is the value of y when x=0.  Anything raised to the power of zero equals one so:

y=ab^0 is equal to:

y=a

So the y-intercept will be a for any equation of the form y=ab^x, or if you prefer it will always be the point (0,a)