Planar Binding

(Player's Handbook v.3.5, p. 261)

Conjuration (Calling) [see text for lesser planar binding]
Level: Sorcerer 6, Wizard 6, Nar Demonbinder 6, Hathran 6, Sha'ir 6, Dread Necromancer 6,
Components: V, S,
Target: Up to three elementals or outsiders, totaling no more than 12 HD, no two of which can be more than 30 ft. apart when they appear

This spell functions like lesser planar binding, except that you may call a single creature of 12 HD or less, or up to three creatures of the same kind whose Hit Dice total no more than 12.
Each creature gets a save, makes an independent attempt to escape, and must be individually persuaded to aid you.