Can fit 12 Commander decks including sleeves without issue.
I have a Backpack of Holding from Thinkgeek:
http://www.thinkgeek.com/product/1e69/
And for my 12 EDH decks I use this:
The backpack has a lot of space to hold stuff; the only thing I don't like about it is having to load everything from the top and sometimes my trade binder annoyingly gets stuck on the inside pockets. Other than that I like it.
The Stack-On organizer is AMAZING for EDH decks and people compliment me all the time on how cool it is.
http://www.amazon.com/gp/product/B004EHY9RA/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
great for sleeved edh decks
I use this for my decks, but don't think it would work for the oversized cards. http://www.amazon.com/gp/product/B004EHY9RA/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
I use this.
Only $12 and it works great.
http://www.amazon.com/gp/product/B004EHY9RA/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
I have 8 decks all in the smaller containers and use the large ones for random cards and lands currently. I could put two in each of the larger ones but would need to make a divider of some kind. I uploaded some pictures to imgur. Also shook it to show there is some play, but no issues if the cards are in sleeves. I have heard of some people putting a small piece of soft foam to hold the cards in place more but I have never felt the need.