I use this script to quickly find files across directories in a project. I have found it works great and takes advantage of Vim's autocomplete by opening up and closing an new buffer for the search. It also smartly completes as much as possible for you so you can usually just type a character or two and open the file across any directory in your project. I started using it specifically because of a Java project and it has saved me a lot of time. You just build the cache once when you start your editing session by typing :FC (directory names). You can also just use . to get the current directory and all subdirectories. After that you just type :FF (or FS to open up a new split) and it will open up a new buffer to select the file you want. After you select the file the temp buffer closes and you are inside the requested file and can start editing. In addition, here is another link on Stack Overflow that may help.