Like getting free drinks and tips at the tavern.
Ventriloquism certainly fits the into "tricky" category. It's the first illusion-ish spell a wizard can get, it does no damage, and its utility is almost entirely based on the creativity of the caster.
Ventriloquism (from Moldvay)
Level: 1 (MU/Elf)
Duration: 2 Turns
"This spell allows the caster to make the sound of his or her own voice come from someplace else, such as a statue, animal, and so forth."So, a couple of things I noticed right off. The range is nice. You can easily send it down the corridor or across a room. The second thing is the duration. If you're clever, you can string some stupid guard along thinking he's eavesdropping on some mouthy PC for twenty minutes!
Another fun factoid: Ventriloquism has no saving throw or "disbelieve" check. This means that the "target" always hears the voice. Now, if they are looking at the wizard locked in a cell when they hear him around the corner, they might be skeptical, but they do hear him.