Well, okay, the original Hellsing was... okay. But then it just went way to far away from the Manga and the animation is way below Ultimate's which in this case actually matters for me. YOu can watch the old serioes but I'd really recommend the OVA's.
Also, seconding Durarara and Bacanno, forgot they got dubs already. Really nice, both of them. And Code Geass is okay but I'd say more up to personal preference. Big O... wanted to watch for quite a while, didn't get to it yet.