Hia,
It is called CDW, Collision Damage Waiver. Be aware though that not all CDW options give you a 0 excess. Your rental company might even describe their 2500 excess as a CDW option (simply because youre not having to pay for the full value of the car if you have an accident).
But in general terms..... yes..... CDW should protect you, just make sure its a full waiver and doesnt have its own excess.
If you do a google search it should bring plenty up. Or clicking the link ive put in brings up LOADS of companies. Ive never used any of them and cant recommend them but there's a choice at least.
http://www.google.co.uk/search?q=excess+insurance+hire&hl=en&sa=2
Have a look at their terms and conditions too, some CDW's wont cover for glass and tyre damage. worth checking!