Potential Spoilers Ahead!!!
#1 Attack Titan
This is a product made by the Good Smile Company. It can be bought on Amazon ($74). The item is made out of Polyvinyl Chloride and it stands at a height of 6 inches.
#2 Armored Titan
This product is one of the most expensive Attack on Titan Figurine Merchandise online. It can be bought on FavorGK ($590), it can be bought together with the Reiner human figurine. It comes with an interchangeable mouth (close or open) head.
#3 Colossal Titan
This is an upcoming extension product to be produced by Good Smile Company. The main artist for the figurine is Takayuki Takeya, a very reputable visual artist. The product is listed and can be pre-ordered on the Good Smile Company Product Page. This marvellous figurine has an estimated bidding cost of around $550. There will only be 500 of these figurines released worldwide, each comes with their own serial number.
The item is made out of polystone, and as can be seen on the images, its visual details are drop dead gorgeous. The figure will stand at around 19 inches tall, living up to the name of the Colossal Titan.