I know this is late but here I go anyway:
The Orange Box:
I'm a huge fan of the Half-Life series and am really looking forward to the next chapter. I also love puzzle games an Portal looks awesome. Plus it includes the awesome looking Team Fortress 2 multiplayer game. I'm sold and it is my must buy game coming out of E3 because despite all the other hype I still think this is going to be the best bang for my buck.
Assassin's Creed:
It looks fantastic and I love the idea of social stealth (Mainly because I don't like the light/dark mechanic of most stealth games.). The sci-fi aspects look interesting and the idea that I will be able to go anywhere and do anything without being a gangster (ok so Assassin isn't exactally a step up...) is very appealing to me. But I'm really ticked at the fact they are pushing the PC version back.
Bu dum! And that's it. Yea, I'm just a PC gamer and I'm very selective about the kinds of games I'm going to put my money down for. I would add Mass Effect and Halo 3 but since I don't have a 360 I cant get that excited about them.