The three Weller soldering iron models for stained glass and copper foil work very considerably in price and performance. Here is some useful information to help you decide which you should buy.
The cheapest of the three is the 80W 'Hobby Kit'. A basic soldering iron which we have found is ideal for copper foil work. We have struggled with this when making leaded stained glass windows as the lack of thermostat means that overheating can casue issues with melting your lead came, unless you are quick with your solder joints!
The mid-range Weller W101d is our reccommended choice, it is not as cumbersome as the bigger 200W, but comfortable to use over long periods and easy to control. It also benefits from a thermostatic control (non-adjustable) which enables easy soldering with far less risk of lead melting. We use these on our stained glass courses at Creative Glass Guild.
Top of the pile is the Weller W201d, the professional choice as the increased power makes it reach temperature faster and hold it without losing heat. It is bigger and heavier, but for production work it is unbeatable. Great when making copper foiled lamps, it speeds up the process of getting the long solder joints looking good.
With the 200w and the 100w, it is important to adjust the tip prior to use. They usually come a little overtightened from the factory. Loosen the tip nut first, tighten until finger tight, then release by a quarter turn. This will allow a little bit of movement in the tip, enabling the electromagnetic thermostat to release and connect the tip as required.