I'll second the size of the Tinfoil Barbs. I've got two over 10 inches. They are fast and active, and grow FAST! If you get Tinfoil barbs, prepare to acquire a 6ft tank to house these speedy giants.
P.S. - Dither fish for oscars are really hit or miss. I've found that anything that fits in their mouth will more than likely end up there. It might take 5-6 months, but small dithers will probably be lunch. Silver dollars are really the perfect dithers for oscars. Their body type allows them to be safe from the mouth of an oscar, and they don't add much to the bioload of the tank.
P.S. - Dither fish for oscars are really hit or miss. I've found that anything that fits in their mouth will more than likely end up there. It might take 5-6 months, but small dithers will probably be lunch. Silver dollars are really the perfect dithers for oscars. Their body type allows them to be safe from the mouth of an oscar, and they don't add much to the bioload of the tank.