GTA IV, Street Fighter IV, Star Wars: The Force Unleased, Left 4 Dead, and Saints Row 2 are the latest candidates for the Platinum Hits treatment. A nice line-up to be certain and a great opportunity to jump aboard and experience these titles if you haven't done so already. It seems like the titles were chosen pretty strategically because with several of the games you have either had a) new content announced and coming soon, b) new content released, or c) sequels approaching.
In celebration of these latest additions to the Platinum Hits Collection line-up, some retailers are offering a “Buy 2 –Get 1 Free” promotion for XBox Platinum Hits Collection titles. This includes the latest additions through October 2009. And while Microsoft is always quick to state that prices in U.S. dollars starts "as low as $19.99," that is definitely not the price for the majority of the titles. You'll be picking up the aforementioned titles at the $29.99 price point. That may be half of a new game's price, but depending on where you shop, it may not be overly competitive with used prices - so it all boils down to preference.
A full list of current Platinum Hits can be found here.