Nostalgia* has been behind almost every movement in urban planning.
1. City Beautiful. Nostalgia for the imperial center, as established in Mesopotamian, Greek, and Roman precedent, and retranslated in the Baroque period.
2. Decongestion (for lack of a better word). Nostalgia for the idealized medieval free city. We can see this in Ebenezer Howard's Garden Cities of Tomorrow and especially in Lewis Mumford's The Culture of Cities.
3. New Urbanism. Nostalgia for the settlement pattern nebulously called "Small Town America". Resultant reduplication of features common to this settlement pattern, with the sole exception of abandonment of the strong grid. Outgrowth of urban theory of Andrés Duany and James Howard Kunstler; informed greatly by Christopher Alexander's A Pattern Language.
4. Landscape Urbanism. Nostalgia for Modernism, primarily as an interbellum movement. Led by Charles Waldheim and James Corner. Nostalgia for Frederick Law Olmsted and Le Corbusier.
5. Traditional Urbanism. (Why is it even on here? Because it's the most cogent response to New Urbanism there is, despite its lack of attention in intellectual circles.) Nostalgia for castle towns (for lack of a better term). Nostalgia for density. Articulated best by Charles Gardner and Nathan Lewis. Informed by Jane Jacobs. Desire to harness urban forces operative in e.g. informal settlements.
There are only three major urban theorists who I can think of who are members of no movement--two of whom are Jane Jacobs and Christopher Alexander--and it's precisely their work that has stayed most relevant through the years. This is frankly because both of their work starts by correctly identifying the problem of the city (a precious rarity in urban theory) and works from there. The third theorist is, of course, Le Corbusier, whose ideas (the Radiant City) have been, by and large, discredited.
* By nostalgia I mean the idea of a historical urban form as the ideal urban form. There's nothing wrong with that--humanity has experimented with a variety of urbanisms throughout its history, and relatively few have failed. Charlie Gardner pointed out that he's trying not to romanticize, and a laissez-faire approach to urbanism should theoretically lead to a variety of urbanisms; one of my larger points, both in agreement and in contrast with him, is that there are a variety of good urbanisms. Of the schools I pointed out, traditional urbanism comes closest to reflecting this--possibly due to its youth.