There's a difference between the modules most commonly used by my code and those most commonly used by me. My code uses DBI more than it uses DBIx::Class, because necessarily any use of DBIx::Class also uses DBI, plus I have a handful of places where I use DBI directly. But *I* most commonly use DBIx::Class because I'd be a damned fool not to.
Off the top of my head, I think that the most commonly used modules here at work, excluding pragmata like 'strict' and 'warnings', are, in no particular order, DBIx::Class, Data::Dumper, Scalar::Util, Test::More, and, unfortunately, Moose.
Why "unfortunately, Moose"? I believe it to be a solution in search of a problem, and I hate all the weird magic that it encourages.