Map (tree) of citations/references I was wondering if there already exists a software/service that allows to build a tree of references/citing articles starting from a selected paper X. For example paper X has a list of references, call it bibliography[X]. This list of references is usually presented in the journal's webpage and, in fortunate cases, the list is also accessible by cross-reference. The idea is then to go to all the papers Y in bibliography[X] and repeat the process for the papers in each bibliography[Y] up to some depth. 

On the other hand, we could also look at the citing articles of X, which is also displayed in the journal's webpage as well as in other resources, e.g. Google Scholar.

In this way the tree of references/citing articles of X up to some depth can be obtained and plotted in a nice graphical framework and perhaps display relevant information of the vertices of the tree like title, doi, etc. In my opinion this would be a very nice and efficient way of discovering new papers related to some paper, e.g. a seminal paper (citing articles tree) or to look into the history of a subject (references tree).

I have been looking for something like that for some time but so far nothing. I think Microsoft Academic Search would have the potential to do this by using the same framework they use for the Co-author path. Also there is this project for JabRef but it is not what I'm looking for.

Edit: 
Something like this would be perfect but unfortunately it is not available to the public.
If you're serious about such a project, I think what you need to do is recognize that this task naturally separates into two parts. It will be very easy to find a good, general purpose and freely available program that suits your taste for visualizing/analyzing/discovering networks in general. I think cytoscape is pretty good, although I've only played around with it a little and many others exist.

Now, the second (well, first) part is to fetch and prepare the input data for the citation relationships of interest to you. You need to be very specific about exactly where you want to get this from and for what subset of articles, since it may not be possible (due to license restrictions) or technically feasible (as noted, the size of the network grows exponentially).