Here's a showcase of all the Zentangle and Apprentice tiles that I've done.
Zentangle tiles are 3.5" square. Apprentice tiles are 4..5" by 4.5". There are also some irregular-sized tiles, and some coloured gemstones featured in this album.
I am a Certified Zentangle Teacher and teach Zentangle classes in Singapore. For more information about that, click this link.