Sony today announced that best-selling PSP titles Killzone Liberation and Ratchet & Clank: Size Matters have officially joined the handheld’s “Greatest Hits” library.

That means you can now pick up either of these great games at the budget-minded price of $19.99. Both are more than worth the cash at this price, especially Killzone, which features support for infrastructure multiplayer and free downloadable content in the form of an extra single player scenario.

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