Intelligence is a very loosely interpreted attribute in 4th Edition
Intelligence (the attribute) is meant to capture a much more narrow concept than "intelligence" (the broad term). It represents the keenness of mind, the quickness of thinking, the rapidity of mental reaction.
It's important to remember that Intelligence contributes to AC equally with Dexterity. A smart wizard is just as good at avoiding being hit as an agile ranger. This isn't because he has a better mastery of language or algebra, but because he can process the information about his surroundings and come up with the appropriate response faster.
It's also worth noting that the range of starting intelligence scores for a character created under 4th Edition rules is 8 to 20. This can increase by up to 10 points for a maximum of 30 at level 28. I'm not sure how much "smarter" Int 30 is over Int 8... I suppose that depends on your own game world interpretation.
Contrast this with, for example, linguistic capabilities of a creature, as language is often a key indicator of "intelligence."
The Id Fiend (Dark Sun Creature Catalogue) has an Int of 13, but is incapable of understanding language. Conversely, the Zombie Cactus (also Dark Sun Creature Catalogue) has an Int of 4 and can communicate telepathically. So, yeah, a talking plant. Also, the Dagorran has an Int of 4 and can't speak, but can understand common. The Balhannoth (Monster Manual 1) has an Int of 3 and is fluent in Deep Speech. Creepy.
The Cacklefield Hyena (MM1) has Int 6 and is bilingual, capable of speaking both common and abyssal, but the Wild Hunt Hound (MM1) has Int 6 and doesn't have any linguistic capacity. Kobold Skirmishers (MM1) also have Int 6 and speak draconic and common.
As far as more objective intelligence scores, Hobgoblins, hardly the epitome of geniousness, can have an Int of 19 at level 3 (Warcaster, MM1).
On an unrelated, but equally interesting, note, the four most intelligent beings in the D&D 4th Edition Universe are Valamardace, Ancient Gold Dragons, Dagon, and Beholder Eternal Tyrant Essences, all of which have an Int of 36 (Vecna and Beholder Ultimate Tyrants trail behind at 34). Tiamat, sadly, lacks any Intelligence score :(