I am also working on a solar hot water system for my house.
For it, I will need a tank, heat exchanger, and pump. I already have a used 4'x10' collector that I bought last summer.
As for the tank, I picked up an electric water heater I was going to modify, but the more I looked at it, the less happy I was with the corrosion and threads/connections on it.
A neighbor was throwing out a 50 gallon steel pressure tank. It is in much better condition than the water heater. I realized that the tanks themselves are both the same size, so I cut off the insulation from the water heater to wrap the pressure tank with. You can read all the details about that
HERE.
I'll still need to find a pump, coil copper pipe around the outside of the pressure tank for heat exchange, and tap into my existing water system, but the project is well on its way!