Martin Fields are the best without a doubt.
They arent cheap, about £10 for a small piece of plastic film!!.
but.
ive used other protectors on pda's etc and nothing comes up to the standard of a Martin fields one.
Ive just installed one on my Vario II and you cant tell its even on the screen, it lets 90% of the light through so you dont loose any brightness/contrast, compared to cheaper ones that dull the screen and make it look washed out.