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

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.