what should I replace when I replace timing belt?

water pump, oil pump, tension spring, some gaskets, ...
Can some one give me some advice?

many thanks

When you do the timing belt make sure to install new crank seals. I dont know what year car you have but mine is an 87 Camry. My backyard mechanic friend and I did a water pump change, replacing the timing belt at the same time. Now 3 months later, I have the crank seal leaking oil. Guess we should have changed the seal when we were in there. For a couple of bux and little extra work its well worth it.

Yes, I agree. While replacing the timing belt, it's recommended by Toyota that you replace the water pump as well. It would also be a wise idea to get at those seals while they're accessible.