Well, I don't consider Lutherans, Congregationalists, or Methodists to be Reformed, but that's me. Actually, I'm not aware that any of them truly consider themselves to be Reformed, versus simply Protestant. Reformed connotes a number of doctrinal points that these churches pretty much reject, especially five-point Calvinism. Of course, you also have Reformed Baptist churches, which I have never understood, seeing that the method of baptism in both institutions couldn't be more contrasted.
Methodists are a resultant denomination of John Wesley, who was Arminian through and through. Now, there are Whitefield Methodists (sound off Clement!) that are Calvinists. These are a part of George Whitefield's Methodism. Another Wesleyan parish is the Nazarene church, which is a really conservative Methodism. They also preach an aberration known as "entire sanctification," which is the doctrine that man can become sinless on earth. Yeah, they departed from Methodism pretty radically here, especially considering that it's quite the extra-biblical doctrine. My whole family on my mom's side is Nazarene, including a couple of "entirely sanctified" preachers.
Lutherans retain a lot of the Roman traditionalism with a Protestant approach to doctrine. Originally, the primary departure of Lutherans and Reformers was the treatment of the sacraments, but the schism has widened over the centuries and now there are a lot of doctrinal differences between the congregations, too many to really address off-hand.
Congregationalism is much harder to encompass because of the very nature of it. Like Baptists, they believe in congregational autonomy. I am a fan of this viewpoint, but at the same time, you get some with really weird doctrines. American Universalism largely grew out of congregationalist churches, from what I understand. Nevertheless, I remain ambivalent about Congregationalism. For one, Jonathan Edwards was a congregationalist. With the Great Awakening, congregations started springing up all over the frontier and the harvest was substantial. God did great things through this system that probably would not have happened within a more strict system. On the other hand, with ever church forming its own doctrine, you had all kinds of different theological systems, each varying depending on the congregation that you attended.
In any case, if you're looking for a Reformed church in America, you should probably limit it to a church that has "Reformed" or "Presbyterian" as a part of their name or statement of faith.
Soli Deo Gloria
Jon