Ross is right,
A good razor type scraper, but not the really big ones, ideal size one is the 4 inch Unger knife, in folds back on itself and can be clamped into a squeegee handle, it's the best knife out there.
The stanley scrapers (with a standard stanley blade in) are ok, but can scratch the glass.
The little hand held stanley one with the retractable-replacable blade is great to have in your pocket for the odd bit of scraping, but not big enough for major work.
Just having the glass wet and using a 'good' scraper is by far the best way of removing the adhesive too.
Regards,
Ian