I have a number of blu-rays. Depends what sort of films you like. The studios are starting to diversify a bit but still reckon we buy mostly action films.
The best picture quality ones I have are
Casino Royale
Pan's Labyrinth
Blade Runner
Pirates of the Caribbean films
The worst picture wise are Dracula and A Clockwork Orange.
other ones I don't have that are staggering quality for their age are
Planet of the Apes
2001
Godfather Trilogy
Some very new films that are er could be better picture wise are
St Trinian's and Mamma Mia they tend to retail for a lot less though.
There are few bad HD prints and tastes vary - avoid the original version of T2 and don't go anywhere near Halloween or the 28 days films . Pretty much any animation done in 4k looks fantastic (even on DVD). All the Bond films released so far have been top quality. I was particularly surprised by From Russia with Love with is absolutely staggering and Live and Let Die which is not one of my favourites and always remembered as the one with garish and weird colours - not any more.
HDTV digest has a good review system. I agree pretty closely with what they say on a lot of films.
http://bluray.highdefdigest.com/reviews.html
Obviously some of the £6.99-7.99 films are bargains if you like them.
P.S. If you can be bothered to wait a couple of weeks Amazon are still selling X-men 2 for the silly sum of £3.98 on blu-ray
P.P.S. People usually get a bit upset about the quality of 80s films in high definition as the colour palette and different ways of doing things really shows up. A lot of them aren't anywhere near as bad as people say and it's just taste.
P.P.P.S. Don't double dip unless you're mad about the film or the version you have originally is shocking e.g. original release of Withnail and I on DVD.
