I made a search over internet but there are so many, I just want to know which are the biggest? How could I find the world's leading? Any suggestions...

Yep, in internet you can find a huge amount. As per my personal experience I would like to suggest you Mastercraft Shutters, which is a family owned and operated business in window shutter field which started over 20 years ago. I had a nice experience with their product and services, so I think they are one among the best.

I have purchased 4 window coverings from blinds.com. One having wood blinds and three having wood shutters. Along with the shutters are the easy-to-follow guidelines in installing shutters. Seeing the result, I can attest how beautiful they are to my house and i'm willing to purchase more.

I support Bryan's suggestion. Even I had good experience with the company which he mentioned. I had panels installed by them and it looks great.

I have purchased from http://www.stevesblindsandwallpaper.com

If you know just what you want, and if they have it, their prices are the lowest I found, especially if you watch their sales emails. Shipping was also very fast.

-Rosalinda

Angela... according to this site...
http://www.windowanddoor.com/top-100-manufacturers-2009-rankings

Andersen is the largest by dollar volume

( over 1 billion annual sales )

Pella is also in that group

Marvin is  in  the next tier down... 750 million to one billion