Here you go!
Progressives- The Center-left party of America. Seen as the "natural party of governance". It dominates suburbs and does fairly well in urban areas as well. They have to walk a thin tightrope between the more moderate and progressive wing. Their main opponent in urban areas are usually Socialists, but they sometimes join up, especially in the South
Independent Republicans- The party of John Anderson, the president of the 1980s. A center-right party that strikes a moderate tone on most things, loving the god they call stability more than anything else. They are usually the main opponent of the Progressives in the suburbs and are popular in any coalition and vote as they are usually classified as "swing votes" both in Congress and their voters themselves. They still get the 2nd most in any elections because of their widespread popularity
Populists- The oldest political party in America, the party of the farmers and sharecroppers, popular in the South and West, heyday was in the 1930s and early to mid-1940s with the rise of Huey Long. The party is economically liberal and socially conservative with anti-immigrant rhetoric common and other forms of racism common. Populists are usually opposite of the AIP/Dixiecrats in the South and Progressives/Reform in the West
Socialists- The "party of the working class" and the most left-wing in the nation. Calls for nationalization abound and they are at their peak popularity in cities and also some rural areas where they sometimes coalition with the populists, especially in the midwest. Socialists have seen an increase in popularity after their collapse as the post-Cold War consensus died. This revival is thanks to opposition to free trade ideas and calls to return to protectionism which is gaining more support now than ever before. On most issues, though they are very left-wing
AIP- The party of George Wallace built to oppose the Dixiecrats, much more economically left and has much more of a national pull. This puts them into constant conflict with Dixiecrats over who is "the true party of the South". This may or may not involve paramilitary groups and good classic voter intimidation of the other side. All other parties in the South, besides the Populists, usually have an agreement to join up and form an insanely fractured government to deny both the AIP and Dixiecrats.
Reform- The "anti-establishment" party created by Ross Perot. The party's biggest concerns are budgetary issues and also trying to destroy the free-trade consensus. Ironically this has lead to an alliance with the socialists on these issues. The Reform Party platform is vague, but they will usually take a populist-lite approach to most things. They are most concerned with government ethics and trying to make sure the system stays clean. Their members are all over the place from social democrats in Vermont to libertarians-lites in Texas and Arizona, to even more standard anti-establishment liberalism like in Minnesota.
Dixiecrats-From the corpse of the Democrats comes a political machine brought to you by Strom Thurmond. Usually allied with paramilitary groups and a smattering of horrific demagogues, these people have an iron grip on some places even with their tools getting taken aways in the 1960s, they are very dangerous and have seen, like the AIP, an upswing in recent years from those who think the AIP are too moderate. They are hated by most people and there are calls for the party to be banned, but they never amount to much.