Fast 'Find in Files' for VIM?

Question

What are some options for getting really fast \'Find in Files\' searching in VIM?

Our codebase is large enough that searching needs to work off an index. grep/vimgrep/et

Answer 1

Something that I use, but not through vim, is ack: http://betterthangrep.com/

It is a perl based tool, and it should be usable in Windows.