Classic parallel clustering algorithms
There's been recent work on doing clustering in the MRC model (a formal model for analyzing mapreduce computations). Specifically, you should look at the work by Bahmani et al in VLDB 2012 on k-means$||$ and earlier work by Ene et al in KDD 2011 on the same topic. These papers have some discussion of the general problem of parallelizing $k$-means, which might be a good jumping off point for what you're interested in.