The two universal animals are the Dales Pony and the Campbell Duck. The Pony is the more expensive animal, at 24 Farm Cash. Remember, if you place the Dales Pony in your Horse Stable, you'll have a chance to breed the Pony for a Dales Pony Foal which can be shared with friends. Meanwhile, the Campbell Duck is cheaper at 16 Farm Cash. You'll receive 1600 experience points for purchasing it.
The final animal is the Ram (Purple Stripes), which can only be purchased for your second farm, as it is part of the sheep breeding process. It costs 30 Farm Cash. While technically, sheep breeding is supposed to only allow the pattern to come from the male, users are reporting that the female's pattern has been carried over to some lambs. Zynga is holding firm to the "father only" story though, so this is most likely a bug, and if you want a "guarantee" of receiving a purple striped lamb in the future, this really is your best bet.
While the Dales Pony and Campbell Duck will be available for the next two weeks, the Purple Stripes Ram will be available in the store for almost a full month, giving you a bit of time to earn up the necessary Farm Cash to purchase it if you can't do so now.