I have a tough time throwing out a lot of different things. I think I could be classified as a hoarder because of the stuff I keep!
If there's something that I know I'm never going to use or have any purpose for in the future I'll try and toss it out as soon as I can, that way I won't get some kind of personal attachment to it.

I have a hard time throwing:
-notes (I used to have a whole box full of letters from friends)
-clothing tags (Ed Hardy tags are just too cool)
-lists (anything I write down to remember)
-paper (I hate the thought of wasting)
-magazines
-clothes (I have stuff from 8th grade I don't wear but can't throw)