If you don't mind an extremely serious manga that has a lot of gore in it, then I would suggest Hellsing. The art is really good and I think it's one of the few books in general out there that really depicts vampires as the terrifying creatures that they are.

That's just my opinion...I fell in love with the series a long time ago, so I am pretty biased about it.

I guess if you want a vampire manga that's kinda cute and romancy......I guess Chibi Vampire is pretty good. Not my favorite series out there, but it's not horrible.