In addition to the Tumbleweed Tiny Homes plans, there is another architect who has some very nice small house designs: Ross Chapin Architects, although IMHO I don't think they are all quite as well thought out as the Tumbleweed designs. Perhaps less experience fitting things into trailerable spaces shows up in the larger products.
Here’s another talented architectural team as far as tiny houses, although “tiny” is relative, some aren’t all that small:
http://www.perfectlittlehouse.com/designs.php
If you admire Prairie Style, “The Aspen” is awesome.