My very first solution was nails in the wall and hanging them on those. This works if a, you don't mind nails in your wall and b, if you have a limited number of rulers.
Then I found this plate draining rack. Which was OK but again limited the number of rulers.
Then there was this solution, an Ikea table top with a small shelf under the glass.
So the search was on for a simple inexpensive solution and I found this little plate rack. It works and for about £5 it is a bargain.
If you click on the picture it should take you to Amazon UK's page where they sell it.
I have 22 rulers on it and there is room for more. It is about a foot in depth so takes up some space but at least I can reach them all now easily. (It has the George seal of approval) I wouldn't put the very large square rulers at the very end of it as I think that might tip it over. It might not, but I am not willing to try. I still have nowhere to store my 36" Olippa rulers as they are longer than my cutting table is wide....
The ultimate solution would be this clear custom made cutting mat and then go back to storing them under the glass. I shall have to wait until Monday to find out how eye wateringly expensive it will be.
I hope this gives you some ideas. And if you have any idea how to store the 36" rulers, I would love to hear them. At the moment I store them upright but they are slowly bowing under their own weight.