I've been looking for a filter for a couple of months, recently I found this one. Sawyer Water Purifier. It is supposed to physically remove viruses with out the aid of chemicals. The best I can tell, Sawyer released this sometime around the middle of 2006. So it's pretty new to the market. I've posted questions about this purifier on other sites but have yet to find anybody that has any experience with it.

Below is an article I found about the Sawyer Purifier.
Just Drink(TM) Water Purifier Essential For Hurricane Preparedness

So far the best price I've found is from Moontrail.com
$79.00 for a bottle, purifier, and faucet adapter.

smitty