A very good optical illusion effect is a Tenyo Special called Sakkaku Scale -Illusion Scale. It is getting harder to find but is now still available on and off from SEO Magic site and on ebay from member magico-japan. If you haven't seen this before you should get one before they are not available anymore at a reasonable price that is.

Definitely a well excuted optical illusion, it's important to remember the steps of performing this trick though.

I've been having a ton of fun with this little illusion. You can take it with you anywhere and break it out any time to have a little fun with someone. It's charming and if you have fun with it then so will your spectator.

I didn't know the proper name for it since the packaging I received was in Japanese. I tried finding it online recently and found it under the name "Illusion Rulers".

This is a great anytime mini-illusion. You can see it performed here:

http://www.youtube.com/watch?v=-oowECOu_CM

There are some cheaper versions of this about, they are commonly sold on eBay.