Linux and Indexed Search

There is lot of options for index search in Linux.
Depending upon what you are looking for the following searches might come handfull-
1)Apropos or man-k
Man -k searches the man pages for the text that you inputted.For example you might want to find the possible commands /and tutors for vim.
man -k vim
returns the possible commands with with description containing the word vim.
For man -k to work you need to do
makewhatis
(to update the index)
2)htdig
You can crawl your intranet and index files in the intranet with htdig.If you want you can crawl the whole internet(think about time and space consideration).
Now you can use htdig to search for files/pdfs/etc.
More information here
3)For local indexed search you can use rlocate ,slocate and locate.
Unfortunately it is not user friendly or should I say 'ID10T free'.
It has all the functions of google desktop,but you must create a database (or index) at start by the command
updatedb
More information here