I'd just like to echo the four or five before me that said Stewart Lee. Stewart Lee. He's exceptional.
My brain is fried at the moment, but some other good ones that spring to mind are James Acaster, Paul Foot, Tommy Tiernan (very different to Stewart Lee though, and to each other). And there's a guy on Twitter and Instagram, Alistair Green, who is superb. Not really standup comedy per se, but close enough.