This sounds cool! Folks I've played with don't tend to ask for specific spells, but there are those they tend to prefer. Popular spells in my experience are ones that are powerful, fight-enders like Sleep, ones that allow the character to control or change the nature of matter, or zip about and do recon stuff. A few examples:
- Summon [creature/object]. Higher level spells last longer/increase the chances of the summoned creature being cooperative or the summoned object being fit for purpose.
- Control [element/substance]
- Transmute substances (eg flesh to stone, vice versa)
- Sense through element/substance. Eg caster can scry on immediate area around open flames within a certain radius; caster can expand their sense of touch to surrounding ground within a certain radius and can sense creatures/objects moving (including their direction and a genral idea of their mass), cracks or cave openings, other geographical features.
- A spell of instant death/permanent banishment from specific planes of existence. The target gets no save and just dies or is permanently removed from the game. Can only be used once per campaign. (This one led to a very ignominious end to a villainous angel who was mid-monologue)
- Teleportation or portal creation spells
I hope that's helpful :)