Various cephalopods are supposed to be as intelligent as household cats.
Personaly from what I've heard and seen about their behaviour in captivity I would rate them more so.
Unlike cats which tend to be just efficient predators in cute fur, cephalopods can solve significant problems and use tools. Which puts them up with the likes of orangutans.
Dissection of the likes of the Humboldt squid have shown the "capacity" of their nervous systems to be orders of magnitude above that of primates. For instance the diameter of nerves in the axion are about a thousand times that of a human and can be considerable in length.
Their eyes are reckoned to be over ten times more sensitive than humans as well as having a significantly broader spectral response. Interestingly the eyes are very similar to that of primates, although squid invertibrate rhodopsin photoreceptor is more like vertibrate melanopsin than vertibrate rhodopsin. Human melanopsin is becoming a hot research topic due to the way it acts upon our biological clock, and thus may help with a number of stress related diseases such as chronic depression. Chronic depression is now estimated to effect as many as one in three people in the first world and be responsable for a significant percentage of unnatural (suicide etc) deaths in those below 40 and likewise untimely (early) deaths in those over 40.
There is an open debate at the moment about squid communication via changing pigment patterns etc. Recently it has been discovered that the nervous system of the squid enables changes to occur an order of magnitude faster than can be seen with human eyes and this has opened the debate on the "channel capacity" of the squids eyes / brain.
From the scientists perspective squid have one advantage in that the restrictions on research for "ethical reasons" are much less than for other research subjects such as "cute furry vertibrates". Part of this is that squid do not appear to experiance pain (atleast in a way we understand), although a number of researchers out in the field seem convinced they definatly suffer distress from observing the "red devils" when hauled on deck.
That being said Mexican fishermen pull up something like 110 million Kgs of Humboldt from the Sea of Cortez each year. This is mainly for the Asian food markets where "squid wings" are seen as a more sustainable alternative to other aquatic foods some of which are in serious decline from over fishing. One reason for this is the highly adaptable squid are filling niches left by the significant loss of vertibrate fish stocks, which possibly means that some vertibrate fish types will not be able to recover and will become extinct. Thus we should start eating more of them not less.