Scrubs, Greys Anatomy, House, ER, NCIS, CSI, 24, How I Met Your Mother, Big Bang Theory, Bones, Suits, Californication and Spooks are all pretty long running.
Also getting there are Homeland, The Walking Dead and Suits which I'm watching at the moment.
I haven't watched every episode of any show, but the ones I've watched the most episodes of are Supernatural and House Supernatural is on its 11th season and still going House had 8 seasons but is now finished