I keep the graded ones in this table I made. I have a few more than when I took the picture, but it's nowhere near full.
The rest are in various holders in the usual cardboard boxes. Some on shelves I made, some on a shelf someone else made for I think a stereo but it happens to fit three shoebox boxes across just fine.
Shameless plug - I have a small box I made in the T card BST that will fit graded cards. All oak and very solid.
Steve B