[development] Where to find free icons?

I'm working on a bunch of file specific stuff, and I've been trying to do some little things to spruce up the file forms. One thing I've done is add a filetype icon... I borrowed some from PHP File Navigator (http://pfn.sourceforge.net). I'm not sure if their licensing allows me to use them, and I want to avoid any possible license conflicts... Can anyone recommend a place to find freeware icons for filetypes... preferably as images... all I keep finding are .ico's.... .darrel.