The Lord of the Rings trilogy (althought it loses points for not having the houses of healing scene in the last film).
Hobbit films are alright for the most part, I appreciate that they are putting in stuff from the expanded universe to tie the relevence of the events in the hobbit to lotr. What is bloody terrible is that they introduce a female elf (this is a good thing as there are no female characters in the hobbit) then instantly put her in a love triangle... (seriously peter jackson?! wtf?). Smaug is amazing.
Harry Potter minus films 3 and 5. PoA missed one of the major plot points of the filmand arguably the whole series (that Moony, Wormtail, Padfoot and Prongs are Lupin, Peter, Sirius and James) and OotP misses loads out (can be forgiven a bit as its the longest book of all of them) but whoever told Daniel Radcliffe to act as if Harry is about to burst into tears half the time was obviously high.
The Godfather 1 and 2. Damn near perfect translation from book to film.