Great answers already! For our daily work, we use 2 tubs, one for the books we are currently using, and one for the books to come later in the guide. I snapped a picture of them and posted them on this thread:
viewtopic.php?f=6&t=5531
For long-term storage, I have one big shelving unit in the basement (super sturdy, not so pretty, Menards's type shelves that are deep and tall

). I bought large rectangular flat clear tubs, one for each year of HOD. They stack on top of one another neatly, and are probably about 30 inches long, 6 inches tall, and 18 inches wide. All of the books for a year fit in them. For the Emerging Readers, DITHOR book sets, and phonics books, I use shallow clear tubs with snap-lock lids. They are probably 10 x 14 x 4 or so. I purchased all of these at Walmart. I stuck white labels on the spine of each book, with a heart and the guide's abbreviation (i.e. CTC, DITHOR 2/3, RTR Ext., etc.). This has helped us re-shelf them later, as the dc often take the books promptly to the room to reread after we've finished them, they love them and want to reread them often usually.

My middle ds knows he can't read PHFHG on up books as they are in years to come for him. HTH!
In Christ,
Julie