"Free Shipping" can work wonders.
Just based on my own behavior buying online - or even through catalogs for that matter, 'free shipping' is a huge draw - and can even be the deciding factor when I have to pick where to buy.
One quick policy note: if you mention 'free shipping' in your ad, when our team reviews your ads/sites, they'll be looking to see the free shipping offer confirmed before they get to your checkout pages.
AWA