Forgive me for resurrecting a long-quiet question, but I've been trying to get the scale of politeness in my head as well. How does this look? (I've put what I think are very literal English translations, to help me remember them)
Formal: "Skulle jag kunna få en glass, tack?" (Could I be able to get an ice cream, thanks/please?)
Polite: "Jag skulle vilja en glass" (I would choose an ice-cream)
Casual: "Jag vill ha en glass" (I want [to have] an ice-cream)
Demanding: "Ge mig en glass" (Give me an ice-cream"
Appropriate if you are mugging someone: "Hit med en glass" (Hand over the icecream)