Suggestions for other effects:
Area that prevents ranged magic. No fireball. But touch and burst spells are OK.
Area that limits physical ranged weapons. Maybe range increments are decreased by 80%(Pick a number), 100ft becomes 20ft. All of a sudden, that long ranged compound strength bow is far less effective as a stand off weapon.
Area where hand thrown stuff works normal but mechanically assisted ranged stuff fails.
Room where all +/- effects don't work but other aspects function normally. That +2 sword of fire becomes a normal sword of fire.
Critter that is immune to any magical weapons or effects. If a weapon has any magical enhancements, the critter is just not bothered by it. Same for spells. But if a spell creates non-magical things that fall, the things can hurt the critter.
Places where dark vision fails but normal vision works as dark vision. Effect is a char with dark vision is blind in the dark but a char with just normal vision sees just fine in the dark. Both see fine in normal daylight. Different variation - Normal vision fails in normal areas but works fine in the dark while dark vision fails in the dark but works fine in normal light.
Agree with others that effects that cause a player to be sitting bored due to missed actions is generally a bad thing. Making same player have to come up with Plan F after plans A-E fail can be a fun challenge.
