Never really thought about, but here's my top 15 (in somewhat of an order):
1) Devil's Reject's
2) Halloween 2 (1982 version obviously)
3) Halloween 6: The Curse of Michael Myers
4) Eden Lake - Not really horror, but I loved it. Definately worth checking out.
5) The Loved Ones (2009) - Hasn't been released in the US. Fuckin brutal!!
6) Mr. Brooks - Not really horror again, but a solid flick.
7) House of 1,000 Corpses
8) The Last House on The Left : Original version
9) Halloween 5: The Revenge of Michael Myers
10) Saw VI
11) Psycho II
12) The Stepfather (Original obviously. Remake was awful)
13) The Poughkeepsie Tapes - Yep, go ahead and give me shit. I thought it was cool
I'm sure I've forgotten some.