I have 10 inch dark wooden stakes with numbers punched into their sides and a list of numbers and plants. BUT.... the only thing that works at all well for me is an aerial photo (taken from our roof or a ladder) of the beds in the spring.Then I print this up on plain rather than photo paper and I circle each plant and label it on this "map." Then I mess my system up by moving plants around and failing to record this anywhere....

The best thing I've found is to use the metal markers and make labels using a Brother P-Touch. Make sure you get one that uses TZ tape. That's the tape that is fade- and weather-proof. I've had mine out for about 3 years with no fading so far. It's expensive, but it's worth it. (I suppose you could put the tapes on wood or plastic markers, but they wouldn't last over time. Even the plastic gets brittle and breaks after a year or so.) Good luck! (If you find something better, let me know!)

You could try making labels out of soda cans. Once cut up into strips, you can write on them with some pressure and they will make an indentation. So it won't matter if the marker etc washes off.
:)