I need my pic to output 3.3V, but I'm not able to use a couple of diods to lower the voltage, while the line is swithces between 3.3V and ground. btw: Fever componts the better.
Most of the solutions mentioned above have a tradeoff with speed. If you have slow speeds, a zener will work or even a voltage divider, but if you need high speed, you'll really need a level shifter. The 74HC4050 is cheap and dirty (and plenty fast) six in a single package if you need that many.
Mr. Nigel is right for an example if you need the pic to comunicate with 3.3v logic level devices i surelly recomend the Max IC, if it's for something more simple the zener could do the trick