GridStream Productions

http://hellsing.pioneeranimation.com/

Highly recommeded series.
This is one you vampire lovers out there should catch.
Addictive as well, a bite from a vampire's embrace

Seconded... very very good series. Books are extremely good as well... though if ya get the same versions I did bit of a bizarre experience reading them the Japanese(?) way i.e. from the back to the front...

... but definitely worth it just for the gun Oficer Seras gets