I loved 28 days later, 28 weeks later was pretty good too i thought.
28 Days later set the benchmark for the whole zombie horror genre. A lot have been done since then, but all seem too familiar now, which kind of makes them forgettable. The intensity and "on the edge of your seat" by 28 days later is, i reckon, unmatched in any other zombie film. England seems to be the best at zombie films.