If you're not using Helm, you're not using Emacs the way it's meant to be used in 2014. It sounds crazy to suggest than an Emacs extension could transform your workflow, but Helm can.

Projectile is cool, but mostly I just use it so I can quickly and recursively find-files in my current project.

I'm torn about using helm. It looks cool and can display a lot of information, but ido seems to disrupt your workflow less, the way emacs masters of old wanted it to be.

I regularly use projectile with helm. I particularly like helm-projectile-grep/ack, which runs grep or ack on the files in the project. Another great feature is the set of projectile commands to toggle between a test and implementation file (assumes you use a test directory structure that mirrors your code's structure), or simply find a file in your tests.

Note that Projectile is about dealing with projects, but Helm is providing the split window UI in the video. Completion like ido, using the minibuffer, could also be used.

(Helm is the sucessor to anything.el http://www.emacswiki.org/Anything)

Helm is amazing. Helm all the things.

One of my favorites is helm-hoogle for completion of Haskell type signatures, function names, etc...

I recommend adding in helm-git-grep if you're working on a git repo. It's how I navigate most code now.