I shudder to mention YLI, because I know that this website is like manna to the Gov teacher's soul. But, whatever... Maybe you don't know... so here is the glittering goodness of this website.
When I don't know what to do, or need some where to start, I go here. They have really great lesson plans that you can use as is, or modify to the needs of your class. I have used many of the websites, particularly the one on Federalism, to give kids activities and discussion points that really get things moving. The dynamic duo that run this website do a great job of getting back to you when you are in need... And are totally enthusiastic about their craft.
There is a model Congress that you can either participate in solo or with a virtual community of schools nationwide. I use the model Congress AFTER we cover Congress, because it does a great job addressing the FUNDING of initiatives; how laws are crafted, etc. However, I have NOT done the nationwide activity because of time constraints.
I have used the virtual voting module, which you can tailor to your home district's ballot... (although I do have the kids visit Project Vote Smart's VoteEasy module to learn more about the candidates before they vote. WARNING: VoteEasy is updated for National Elections, only. Boo.) Anywho, there you have it. Where to do when in doubt.
Photo via Flickr/Ted Eytan