Robin, at a high level you can have:
Spanish, Gallic or German formed cavalry
Spanish and Numidian skirmish cavalry
Skirmish javelins and slings (think Numidian, Gauls Spanish, Germans, Illyrians, Thracian, Greeks)
Allies from Numidian, Pergamene and Armenian lists, plus a couple of units of Illyrian Warriors (so you could have Thureophoroi (Peltasts) and skirmish bows from the Pergamene list, Cataphracts from the Armenian list, as examples)
Of course, the core of your army needs to be Legionaries!
Hope this helps,