The New York Times has a delegate calculator. This consists of a slider which allows the user to set a hypothetical percentage of delegates that Obama (or Clinton) will win in the remaining primaries, and returns the percentage of the remaining uncommitted superdelegates that candidate would have to get in order to win the Democratic presidential nomination.
Of course, it varies linearly -- for each pledged delegate a candidate gets, that's one less superdelegate they need. Since things are phrased in terms of percentages, it's not quite so simple -- there are 217 pledged delegates left and 225.5 superdelegates with unknown preference. (Half a superdelegate, you ask? Democrats Abroad get delegates that each get half a vote.) So for each one percent more of the pledged delegates a candidate gets (that's roughly proportional to the popular vote, although rounding and the fact that delegates are assigned based on historic turnout as opposed to current turnout alters that), they need slightly less than one percent less of the superdelegates. (Don't try to do the arithmetic; it doesn't seem to quite work out, because I suspect the superdelegate counters and the slider-makers aren't constantly talkign to each other.)
This is an interesting wya to display the linear dependence; a graph or a table would seem more obvious, but with computers one isn't bound to static displays as one is on paper.