exactly last year in May, OLZ desigend his 5x5x3. I built it and presented it in this forum in Juni 2009.
I got the inspiration to build it in the dimension of a floppy, as I saw the 4x4x1 in floppy size.
I used the print service of Karl-Heinz to made the pieces smaller (60% of the original size).

Video: http://www.youtube.com/watch?v=MFwD5gyQrOQ

I have stopped collecting cuboids with one dimension greater or equal to 5.
That saves a lot of time and money.

But now I might rethink it...