One modern incarnation of the debate between nominalism and realism is to be found in philosophical arguments about sets.  There are two ways of characterizing a set: intensionally, through description (e.g. the set of all inhabitants of London, to use an example of Russell's), and extensionally, which is just a list of the members of the set.

Joshua Landy just posted a very interesting blog entry here, partly on how the fallacy of conversion tends to work in Derridean argument.  I am no longer enchanted by Derrida -- I've been... deconverted? deprogrammed? -- but I was prompted to defend him in the comments to that post.