If you are non-eu you need your passport and your resident permit when you travel.
A friend was stopped at the German border and after 6 hours of trouble was escorted back to Switzerland with a nice warning about going to Germany again in the next 10 years. When he told me that story I looked at the Schengen agreement and remember I found somewhere that you indeed need your permit AND passport when you travel.
Yes, most of the time they don't check when you travel in schengen countries but the law is the law.
That's my opinion about non-eu, if you are eu maybe another eu person can tell us if you can travel without passport in the schengen area.
Good luck,
Leo
May 9, 12 23:39