Algorithmically, it is always interesting to get good solutions to the 
rank aggregation problem for different metrics on permutations and partial 
lists.  Currently, we have a good understanding for Footrule and Kendall 
tau. But, there are several other permutation metrics.

Recently, I have looked at some extensions to metrics on rankings:

  http://portal.acm.org/citation.cfm?id=1772749

It may be interesting to some people. There are several questions that are 
yet to be answered.  This may a different topic.