Aye, didn't know that.
Dara O'Briain - Okay, I like him but he's pretty run of the mill.
Bill Bailey - one of the all time greats. Went all the way to London last year to see him and he's even better live. I don't think he deserves to be called intellectual as such, but he's certainly in the very top of the intelligence scale among comedians. I love that instead of pandering he tries to open people's minds a little by talking different languages and talking about different geographical locations.
Bill Hicks - Really like him. Slight intellectual bent, but above all he plays on the "open your eyes to what's really going on", battling naiveté.
Dylan Moran - Haven't seen him that much, but I'd stick him with Dara O'Briain.
Of these I'd say Bill Bailey is by far the most intellectual, although his style is still a very approachable and easy to follow kind of intellectualism. Bill Hicks's jokes are also intelligent I would say.