Before getting a Kill-O-Watt or WattsUp (my choice for measuring individual small loads), you might want to think about getting a TED (The Energy Detective). Then you can measure the whole home or individual circuits.
I'm no expert but I have looked into solar a fair amount and the best bang for the buck in somewhere like Wisconsin would simply be in preheating the water going into your domestic water heater. The colder the ground water the more effective the preheat will be. It would probably do most of your summer hot water and a significant portion in the winter time. Domestic hot water for your local might be one fifth of your gas bill. If your annual gas bill was $1500, then DHW might be $300 and of that you'd probably save half. A system like that might run you $4K and the rebates and incentives vary widely and change often. Solar home heating would probably have an even worse return. The best return is on caulking.
