Plastic Fantastic – an online shop for plastic filaments – has an interesting material in their plastic arsenal: Flexible – Rubber like plastic filament. The material is extremely elastic and can be well used for RC car tires for example.
Warning: The material is still experimental, so the results may vary. They have only been able to print under certain conditions, which is noted on the product page. The material doesn’t stick to blue tape or kapton tape and the support material is difficult to remove. Therefore the material is suited for simple designs. However, this points to continued material development of materials for entry level 3D printers that bring new properties and consequently more applications to the fore.
The material retails for little over $50 per 1.1 pound. Read more here and here.