Am currently poking my way around Jade Empire, Prince of Perisa: Warrior Within and Ninja Gaiden again. Thinking about checking out Beyond Good and Evil and Eternal Darkness, since they both sound really interesting and different from mainstream games that are pumped out.
A rental might be better, since Assassin's Creed can be unforgivingly repetitive and that the combat system is pretty easy to master after your first or second mission. It felt like a long chore to play after the first thirty minutes of gameplay to me, but you might like it. Still recommend that you rent it first to see if the gameplay appeals. If there is one thing I can comment positively on though, it's got to be the climbing and free roaming. Oh, and assassinating people at random.
The other two games though are definitely something you should check out. They're pretty fun, especially Portal.