I haven't tried it, but a quick search on CPAN yielded Module::Dependency::Info, which sounds like it might do what you want. It can't get everything, since it's possible to hide dependencies inside an eval, but it will probably be better than the recursively-grepping home-brew script I use to do this.

Out of curiosity, what are you using this for? My little experiment grew out of an attempt to merge POD from required modules into one gargantuan page.

/s