The best screen proctector, I've ever used for the Z is the overlay brilliant, so clear you don't even know its there most of the time.
It's a little pricey (¥1550) but well worth it in my opinion, I used them both on the C760 and the C1000, and have friends who use them on their clie's.
NOTE: don't get the overlay plus, it has a matt finish and makes your screen look foggy.
Brando used to sell the overlay brilliant, not sure if they still do
Stu