littlemonk:

As you can see from the other responses, it depends on the problems you tend to need to solve. Having said that, my list of "indispensible modules" is: Spreadsheet::ParseExcel, Spreadsheet::WriteExcel, DBI, DBD::ODBC, DBD::Oracle, and DBD::SQLite. There are dozens of others that I also like to use, but since I do a lot of data spelunking and generating reports for users, these are the ones that I use in most of my projects.

...roboticus

When your only tool is a hammer, all problems look like your thumb.