This topic has interested me for many years. Longtime ASA members may recall an article I wrote about modern Jonah stories: http://www.asa3.org/ASA/PSCF/1991/PSCF12-91Davis.html . I've never found any particular argument about the historicity of the biblical story very convincing, though I would not want entirely to rule it out.

The most interesting interpretation I encountered has already been stated in this thread: that Jonah, like Jesus, was actually dead for part of the time he was in the whale's belly. I didn't find that argument very often, but it was endorsed by at least a few commentators who wanted to push the parallel Jesus makes. The arguments against that possibility, given here, seem pretty good to me.