I have two sets of opposites cards. One from Kizclub. I printed cards out, laminated and staple them twice on the left side, like you can see on the picture.
The other set I bought on sale from Borders. (Before they closed it!). It is "Dora The Explorer".
As you can see from the picture, these cards are used a lot. Eaton had so much fun sliding them up and down. I think it is worth to purchase them for learning purposes. Great pictures that keep your baby entertained.
Have a great day!