World Of Warcraft too, although Blizzard put a Warcraft skin on it. =\They did make a new one and called it Diablo 2.
Three ex-Blizzard employees founded Arena.Net and created Guild Wars.The core programmers which made Diablo and Diablo 2 'left'(got layed off) Blizzard and started their own company, which produced Hellgate London. From what I have read this game has a lot of elements of Diablo 2, but is played as an FPS in a techno/sci-fi environment.
You could also give Guild Wars a go, which, from what I heard also has a lot of similarities with Diablo 2.