I stumbled across an interesting post at a news site in New Jersey, where the writer mirrors comments I've made about how a political party isn't the only way that a movement can enact change. Centrists can learn from some examples of this
The Tea Party is an example of this, although they are, of course, mostly working through the Republican party. To a lesser extent, the so-called 'netroots' types, very liberal for the most part, have had increasing influence on the Democrats. The post mentions women's rights and civil rights, as examples, to which I would add the progressive movement (not to be mistaken with those who would call themselves progressive today).
The progressives peaked with President Theodore Roosevelt, and some political parties did appear for a time, but their views were largely co-opted by the Democrats and Republicans of the time. This shows how a movement can find other ways besides party formation to bring change.