from Tyrone Shoelaces
Keep one of those Bounty dryer sheets stuck in each boot. (not while you're skiing of course
Seriously, after a day of skiing, stick one sheet into each boot and just let them hang out in there until you ski again. When putting your boots on in the morning, just take the sheets out, leave 'em in your car, then stick 'em back in at the end of the day.
Helps to absorb a little moisture but more importantly keeps 'em smelling fresh.
Also spraying with Fabreeze works ok too...
The above methods are just for treating a the symptoms though of a bigger issue. The stench is caused by bacteria/microbes that have taken up residence in your boot.....so just simply not using the same ski socks two ski days in a row and other common sense stuff like that can help keep the problem at bay as well