You can also click the following link to create your own Mii. When you are done, press Print Screen and then select Edit-> Paste in program like Paint.

For full window click here

There are also newer versions of Mii editors availiable on the web. Their big difference with the one here is that they let you create a real Mii, which then you can get to your Wii. Just check the following links for now.

http://www.miieditor.com/ 

http://aj.heypoorplayer.org/mii/