I remember when I first started with Drupal. There was just a handful of modules compared to today. I want to say something like 600 or so...
In fact, there were few enough, I had printed the whole list of all top Drupal modules and took a stack of paper home to read about each one. Fast forward to today's module count and it's coming close to 6,000!
Can you say "Holy metric ton load of Drupal modules to search through Batman!" How do you really know which are good and which are bad?
To start, keep this in mind. Drupal is open source, and pretty much anyone can contribute back to the project. While Drupal's future of version control will place a few more barriers to entry to just anyone submitting potential duplicate modules, (therefore preventing the wonderful module of shame issue ) you still don't really know which modules are coded well and which are not - unless you dig into their code.
So, the quick answer to this problem about knowing which are the top Drupal modules, is to use Drupal.org's /project/usage stats. This is the one place you can see which modules are used the most by the most sites (at least those reporting back to Drupal.org).
In this video, I start at number one and head down to module 50 within the usage stats. I've not worked with all of them, but I'm familiar with what most do. I provide an overview of the modules and what they do within Drupal.
If this approach is a good one, and you'd like me to keep going, then please leave a comment on this posting!