I have not used in-room babysitting; will the next trip on our anniversary. I hear a lot of good things on these boards about KIDS NITE OUT, but everyone I know IRL uses (and LOVES) Fairy Godmothers--including my sister. People use the same sitter over and over, but that sitter varies from family to family. Makes me think they have a ton of good sitters that everyone wants to keep using the sitter they had last time, but each family has found a great sitter the kids love. I'm sure you can't go wrong either way.
Info from the Unofficial Guide:
KNO: male & female sitters; minimum charge 4 hours; 1 child $14, 2 children $16.50, 3 children $19, 4 children $21.50; transportation fee $10; starting after 9 PM +$2 per hour; cancellation deadline 24 hours prior to service when reservation is made; payment amex, discover, mastercard, visa; gratuity in cash; will not transport children in private vehicle, take children swimming or give baths.
Fairy Godmothers: sitters mothers and grandmothers; minimum charge 4 hours; 1 child $16, 2 children $16, 3 children $16, 4 children $18; transportation fee $12; starting after 10 PM +$2 per hour; cancellation deadline 3 hours prior to service; payment cash or travelers checks; gratuity in cash; will not transport children, give baths, swimming at sitters discretion.
There is also All About Kids.