Worthwhile checking out Amazon.co.uk - some excellent DVDs under the banner of `3 Fox DVDs for £30` / `2 Warner DVDs for £20`.
However, they don`t commit you to the multibuy offer - you can just pick up one for a tenner if you prefer!
Titles include X-Men, What Lies Beneath, Titanic, The Gift - and the list goes on.
I know that you have to pay extra for P&P, but at least you know the title is in stock when you buy it, and I`ve never had any problems with the service from Amazon - in fact, I think they`re one of the best online DVD retailers around.
Cheers