Cluster algebras and triangulated surfaces. Part I: Cluster complexes
  We establish basic properties of cluster algebras associated with oriented bordered surfaces with marked points. In particular, we show that the underlying cluster complex of such a cluster algebra does not depend on the choice of coefficients, describe this complex explicitly in terms of "tagged triangulations" of the surface, and determine its homotopy type and its growth rate. 
Sergey Fomin, Michael Shapiro, Dylan Thurston