A hyperlinked version of the code with suitable index pages makes finding the source code for a given function/declaration much easier.
I have been trying my hand at automatically hyperlinking the source code to the BSD Unix kernel (200,000 lines, 6 Meg).
Generating links into the source is not too difficult with a Perl script that calls ctags to find the location of the C symbols.
Generating links out again is difficult; a C parser is needed. I haven't had the time to do this.
The result of the work is here.