Okay, so a bunch of these have already been listed, but I am a huge sap and will cry at pretty much anything...
-Beaches (I love this movie and always cry at the end)
-Steel Magnolias
-City of Angels (no matter what, I bawl like a baby)
-My Life (I am such a sap I bought this movie because it's that good)
-Titanic
-The Notebook
-In Her Shoes (my sister & I are that close)
-Star Trek: Nemesis (yes, I am a nerd, but only the Star Trek fans may get this one)
-A Walk to Remember
-The Sisterhood of the Traveling Pants (when she goes to the dad's wedding)
As well as probably most Disney movies ever made. Like I said, I'm a big sap.