How is that no one mentioned ido?
Think iswitchb on crack. For files. With history. With fuzzy matching.
C-x b NSObject # no match, I guess I don't have it open. Switch to files with ... C-f # Minibuffer: ~/projects/foo/NSObject # no match, obviously, it's in some crazy directory. I'll wait a second ... # Minibuffer: /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS2.0.sdk/System/Library/Frameworks/Foundation.framework/Headers/NSObject.h # YEP! ENTER
That's right, it went and found a system header file for me. I only had to find the first one, then it remembered that files I want might live there. No config, no project files, no tag files, nothing. <3 <3 <3