I think on standard tyres recommended pressures are about 35 psi.
With lower profiles you will want to go higher.
I run as above... any less and it feels all squishy and wandery (does that make any sense?) and tracks white lines and tar lines in the road. Any more and it tends to scrub out on corners, and feels way too slippery in the wet.
If you're running 205/40 17s goto 35 psi all round then experiment, you'll find the front pressures really have a noticeable effect. Find something you're comfortable with. And don't forget it rains from time to time
It will depend on your choice of tyre, how you drive, what suspension mods you have etc.
Cheers
GeeTee 8)