For quite some time Amazon was selling refurbished Kindle devices at a discount:
First generation Kindle for $149.00
Kindle 2 for $219.00
Now you can also get refurbished Kindle DX with 9.7″ screen and PDF support at $90.00 (18%) discount for $399.00.
It should be noted that refurbished Kindles come with the same 1 year warranty as new ones.