Just wait to buy the best of the best that the PS3 has to offer in 2008. And by only having a PS3 all great multi-plat games that you get will be PS3 games as well.
Seriously, get Uncharted but outside of that you shouldn't have to think about what games you will buy for the PS3. You will just end up buying the ones you need automatically.
Point is by years end, you will have at least 12 great games without ever having to make a hard decision about what games to buy.








