Best Search Engines for books, papers, pdfs....

I know that on google.com we can find any thing very easily.....but sometimes, we find that google is a not returning the right stuff which we are looking for and I experienced the same one time.........the story goes like this......one fine day, I was searching for a particular book(pdf version) and could not find it on google....to my suprise, I found it on a different search engine(see below for link)...so thought these search engines might help you when Google can't help you.....very rare though ;)

So, here are those links...

http://gigle.ws/

http://gigapedia.com/

mee,

RaghuRockz....