I have used quidco for years and earned many hundreds of pounds with cashback.
For those who haven't used quidco before, you don't buy from quidco, you enter the holiday site through quidco.
Some examples of current cashback offers
Laterooms- 10%
Hotels.com- up to 10% back( this means that there are several possible offers)
Expedia- up to 12%
Easyjet holidays- 2.4%
Accorhotels- up to 10% ( have seen this as high as 15% in the past)
TUi-up to 4.5%
No 1 lounges - up to 11% back
Hertz- 7%
qatar airways- 2%
holiday extras airport parking- up to 38%

The rates do change quite regularly. There are hundreds of travel cashback offers. Check them all
here

Some tips- don't make your choice on the cashback deals. Always research in your normal way for the best deals and then check to see if there is a quidco deal from the company. You MUST delete all cookies before making the purchase as the companies pay c/b on the basis that you found the deal through quidco. I actually have a browser that I use solely for quidco. If there is any evidence that you found the deal without quidco, the money won't be paid. I always look on quidco c/b as a bonus. Some folks complain that they didn't get c/b but I do think that they may not have deleted cookies. I have only lost c/b once before and it was doing exactly that. Cashback can take months to be paid- I got £33 cashback this week from viator for trips taken last October! Usually I get money 2 0r 3 months after a holiday has been taken. But really, its money for nothing!
Of course there are c/b offers on many other things apart from holidays!
Have you had a good deal through a cashback site? Have you found any good ongoing deals you can share here?