Due to a numbering error, I apparently did five spells in the last post. D'oh! I suppose that's what I get for trying to cobble these things together during lulls at work. Anyway, that leaves us with three more spells to round out the list of a dozen.
10. Shield: This is a pretty potent defensive spell, particularly at low levels. It's as good as mail and shield against melee attacks, and plate and shield against missiles. Since it lasts a full 2 turns, it could be cast in advance of an anticipated combat encounter. As effective as it is, though, I don't think I'd want it as my character's only memorized spell at level 1, because all it does is make the magic-user a little better able to engage in mundane combat. Cast Shield, stand back and throw daggers, or if you've got more guts than brains, rush into melee. Yeah, it increases survivability a bit, but it's not bringing anything to the party that fighters, dwarves, and clerics don't already do better. I like it a lot better as a secondary or tertiary spell, to keep the magic-user safe while he casts other spells or uses magic items.
11. Sleep: This is, hands down, the "nuclear option" of 1st-level spells. 2d8 hit dice of creatures, right out of the fight just like that, no save. The range is a whopping 240', which is farther than characters can even see in most dungeons, and beyond the range of all but the most powerful missile weapons.
Unfortunately there's a lot of ambiguity in the spell description. It specifies that lower HD creatures are affected first, and in the example of combat elsewhere in the rules, the characters make a point of staying out of the affected area, heavily implying that it does not discriminate between friend and enemy. That seems reasonable, since it would be contradictory that the caster should be able to choose between friend or foe but not between weaker or stronger targets. This is never stated explicitly in the spell description, nor is there any area of effect given. So, let us turn to the Mentzer rules, which give an area of effect of 40' square. We have an area of effect 40' square, which may be cast up to 240' away, in which the lowest HD creatures, whether friend or foe, are affected first. That sounds workable.
A thornier issue is how to account for character levels when calculating how many HD of creatures are put to sleep. Neither Moldvay nor Mentzer has anything to say about whether or how character levels equate to monster Hit Dice. Here, I have to look all the way to the AD&D 2nd Edition Player's Handbook, which states that "The number of creatures that can be affected is a function of Hit Dice or levels." Not entirely satisfying to have characters become immune to the spell at 5th level, but I don't have any better ideas.
At low levels, Sleep, with its lack of a saving throw to avoid the effect, is probably the spell most likely to result in a TPK when used by enemy casters. The average HD affected is 7, which is enough to knock out an average party of 1st level characters, and with a lucky roll a lowly 1st level enemy magic-user could wipe out a party of up to eight 2nd level PCs, or even four 4th level ones. (At 4+1 HD, only one creature is affected, but below that, the roll of 2d8 applies - another oddity of the spell description.)
12. Ventriloquism: This is one of the shortest spell descriptions in the rules, and I like it that way. No variables, no situational modifiers, not really even any game mechanics to describe the effect beyond range and duration. It makes the caster's voice come from somewhere else within 60', and the rest is up to the DM and players. Presumably the sound can be any noise the caster can make with his own unaided voice, from clear words to animal noises, from a whisper to a shout. Also, there is nothing that says the location from which the voice is to emanate must be visible and accessible.
Besides all of the possibilities for diversions, misdirection, fake hauntings, talking animals, giving orders to the villain's goons right from the villain's mouth, disrupting speeches from pompous nobles, delivering messages from "the gods" to the gullible, and other zany hijinks, you could also use it to convey a message to someone trapped in a room or cell (though not receive a reply) or to whisper a secret in the ear of someone 60' away. With the spell's sparse mechanics, there's no other limits but imagination and common sense. It's up to the DM to decide how creatures react, which can make it a fun spell from that side of the screen too.