Any noise filter that has been designed for
use with X10 should be fine. One of the
cheapest options is the X10 Pro XPPF. It
is only rated for 5A, but this is way more
than enough for your router. While you are
at it, you might want to get several of
them for use with other electronic
equipment. You can get it for $14.99 at
Automated Outlet:
http://www.automatedoutlet.com/product.php? productid=155&cat=43&page=1
They have a very competitive price and
provide good customer service (with all the
recommendations I have been giving them it
is too bad I don't get a kick back
).