Thog from The Order of the Stick, who proves to be the exception rather than the rule when it comes to half-orcs. Of course, being a barbarian, INT was his dump stat. A later introduction is the dragon/ogre hybrid Enor, who appears to be very slightly more intelligent than Thog, and possibly even stronger.
Of the Order itself, Roy finds himself constantly battling this stereotype. He could have been a wizard like his father wanted, but he chose to become a fighter instead.
Crystal of the Thieves' Guild is an inversion of the typical stereotype. She's a petite, lithe girl who's both the Guild's deadliest assassin and dumb as a rock. Her boss, Bozzock, is a hulking half-orc who has to do Crystal's thinking for her.
In The Adventures of Dr. McNinja this is shown to be Martin Monster's (a Captain Ersatz of the Hulk) fatal flaw, in that his Super Mode leaves him dumb and easy to manipulate, resulting in him accidentally betraying his college buddies and leaving him in debt to Mafia leader King Radical.
It's also an inherent effect of having too much muscle. Eventually the muscle forms into a jetpack, and when you're flying around all the time your oxygen-starved brain becomes less efficient, causing you to speak solely in bodybuilding cliches.
Fighter, Black Belt, and Bikke in 8-Bit Theater. Black Belt is a Genius Ditz, a master of hand to hand combat who can't navigate a straight line, while Fighter and Bikke are all around morons (though still smarter than people give them credit for); Among other things, Bikke insists on being known as "The Claw", on account of the fearsome claw in place of his right hand. Except he actually has two perfectly normal hands, at least until he acquires a claw that he simply slips on. Meanwhile, Fighter simply doesn't understand that Black Mage hates him.
Curse Quest: Averted somewhat with Mogarth, in his original depiction in "The Kobold's Dungeon" he definitely fit the bill, smashing through doors without regards of what is on the other side. However in his updated version he seems to be more socially awkward and inattentive, but not outright stupid.
Death Elves in Elf Blood tend to get this treatment, having absorbed some dwarfy/orcy qualities from other fantasy lines. A possible exception is JN, who is strong and has not yet been shown to say anything profoundly stupid. He hasn't exactly been shown to be doing anything unduly smart, either.
Homestuck: Eggs and Biscuits, in the Midnight Crew intermission, are described as "morons, but dangerous morons". Biscuits in particular thinks hiding in an oven until the timer goes is a form of time power.
Nick in Schlock Mercenary has trouble with numbers above 1 and has managed to misunderstand a great many situations. He makes up for it with a good heart, a bottomless supply of loyalty, and being the size of a caravan. Shep was like this too in the early strips, but Divergent Character Evolution gave him at least a modicum of intelligence.
Kurudan from Tower of God, a literal minded big guy who doesn't even know who or what he is fighting half the time.
Girl Genius: R-79, an incredibly strong construct and prisoner in Castle Heterodyne, though he does clue into some things a bit faster than some of the other prisoners on occasion his normal solution to problems is to destroy and murder anything in his way.