I used Ack a lot when I was coding Perl (it's been a while). After I switched to Ruby, I used rak [1], which seemed easier to use most of the time, and nearly identical.

However, when you just want to find stuff fast, it's annoying to have to deal with Perl/CPAN or RVM/Rubygems, especially when the dependencies are not installed on your server/workstation.

That's why I've switched to silver searcher (ag) [2], as it can be installed with any OS package manager (brew, apt, yum).

[1] http://rak.rubyforge.org [2] https://github.com/ggreer/the_silver_searcher