I never used to bother with using a toner, but lately I've been using Avalon Organics Lavender Hydrating Toner because of the salicylic acid in it (salicylic acid is good for oily skin). It's been pretty good for preventing and treating acne. It's $21 at Health 2000 stores, and is intended for sensitive skin.
Other options for toners $15 and under: Sukin Hydrating Mist Toner $12, Natural Instinct Toner $12
$20 and under: The Herb Farm Rejuvenating Facial Toner $18.60, A'kin Orange Blossom & Chamomile Toner $17.90, Weleda Iris Facial Toner $18.70