What were the biggest hidden clues in OoP?

[gsanderson at cfl.rr.com]

No: HPFGUIDX 96007

Just curious what you all think are the biggest hidden clues in book 
5. This means information that JKR mentioned in passing that will 
become important later in the series. My top 3:

1. Prof. Umbridge uncovers that Snape has been at Hogwarts for 14 
years which means he joined right after LV's demise.  This implies 
that he played a big part in the events, but who's side was he on?

2. Neville's parents in St. Mungos are trying to get a message to 
Neville using the gum wrappers (my guess)

3. Harry can do magic without a wand (Lumos!)

Other thoughts, anyone?
Kristen