We had a tiny dent in a hire car recently (done by someone else in car park) for which Avis stung us nearly £500 
Their own excess waiver would have been 19 euros a day (or about half the excess charge, over a 2 week rental 
) but I got cover from \link{http://www.carhireexcess.com/\carhireexcess.com} before we went; it was only £25, & they have settled the claim in full within a week!
Highly recommended.