Spartans are pretty decent for pinning units, because they have great stamina and staying power. They won't beat a Makedonian-style phalanx from the front, but they'll hold out for a while. Also, Peltasts. Use them for shooting phalanxes from behind whenever possible (phalanxes are priority target #2 for Peltasts, Number one being Elephants). They'll probably cause less casualties by friendly fire than slingers, and be more effective than archers. You can also use Akontistai for this, especially seeing as they can lob even more javelins, but they may rout upon (accidental) melee "contact" with enemy units, so you'd have to be extra careful with them. Peltasts are also good flankers unless you've got something better.
If you like using mercenaries, Botroas are excellent flankers against light and medium phalanxes. Or if you have too much money, Tindanotae. Also Galathraikes and really just about any kind of Thrakians, should you get your hands on them. Thraikian Peltasts carry missiles and AP swords and are useful for attacking elite phalanxes from behind.