I've got the same basic offer as James -- 25% to 35% depending on how much you spend, but if anyone needs it, my code is FVM3453V.
In my experience, the best coupons STP ever runs are 40% off existing prices, plus free shipping, but coupons that apply to most of their inventory are rare. Usually the lower the % off, the more of their inventory is valid for the deal.
The 35%/free shipping is usually a sweet spot for most of the gear you want actually being valid. Hard to tell without checking out the site if this one has free shipping or not -- it looks like it might for orders over $100.
There are rare 80% off (original prices), plus free shipping, coupons that have very limited inventories -- the only things I've ever purchased on those are wool socks, Nikwax products, and cedar balls/cubes to keep wool clothes from being moth kibble.