In vim, there is this amazing plugin called command-t, that lets you fuzzy-search through all the files in your project. We have a fairly large rails app with a ton of files
Depends what you mean by fuzzy matching. Most fuzzy matching is inherently slow, but some lightweight, pseudo-fuzzy algorithms are pretty fast. Generally speaking, you're probably better off with a regexp search, not a fuzzy-match search.
Anyway, there are two parts to the question:
Icicles can help with both:
Project definition, management, etc.
Searching a project or parts of it:
Searching file content (and search-and-replace)
Locating files