Dont think this has been out on British TV yet but there's a great series called Dexter. It's about a blood splatter analyst who works for the cops but also has a secret life/fetish as a killer too.
I've only watched the first episode this morning, but i have to say it's really good!
Well I just HAD to find something to replace Heroes and thought i'd go for something non-sci-fi so i didn't compare too much.