You guys are always talking about the Assistant or such. If only this little guy had an opposable thumb [or bigger, stronger paws], then he might get that door open 
my pit could open windows, doors, and the fridge. what a pain lol. rip fox
My cat could open doors with the bar handles not the round knobs.
he can open a door with a quick sweep of his paw that is ajar, but a knob like this is obviously impossible, haha.
It's funny how easily a critter can walk up to a door that is essentially closed (just not latched) and stick his paw in there to open it without pause and then when he exits he'll simply headbutt it. How do they tell the difference between open and close/enter and exit?
We once had a big doggie named Barney and he has a dark secret, an undying love for our fridge. He's very intelligent and would masked his affection towards the cold box while we are around unsuspecting of his grand scheme.
However...
Sometimes we keep the dogs in while we are out and that usually spell disaster. He would open, ransack and empty the fridge together with his 2 mates.
Angry cleaning and mad burst usually ensured later.
To avoid expected onslaught while out, we decided to chain and padlock the fridge instead of them 
I once had a keeshond (supposedly a smart breed, but requires the effort to train) that not only took a chunk out of the motorcycle seat but also managed to chew a chunk out of the living room carpet. That was the last experiment with dogs. We just couldn't give him the attention he needed.
I generally enjoy the wild aspect of cats. I don't want the Fancy Feast cats. I enjoy watching mine catch birds, rabbits, rats and just acting wild yet still domesticated in a sense that they remain within our boundaries all on their own. I know cats have a negative stigma when you hear about the crazy old lady with 15 cats, but you might be surprised what a cool cat can do as a pet
Want to see intelligence?
Observation, trail and error and a good memory 
As all cat owners know once they learn something it’s impossible to break that habit!
Mine will open a door to a closet just to walk in and out not really even knowing why he wanted to open the door in the first place but if you close the door he will go right back and open it!
My cats open doors too.
Our family dog (German Shepherd) used to answer the phone. It was the old fashioned type where the handset rests in the cradle and it used to be kept on the floor next to the couch. As soon as it rang, Baskerville would nudge the handset off its perch and start barking. The amusement value of this trick very quickly wore off for my parents, and many an unwary caller got quite a surprise.
One day the call was for Dad and he had to spend five minutes talking important business with an ear full of dog slobber. I seem to recall it was about then that he finally fixed up a high shelf to put the phone out of reach..
There's a reoccurring skit on late night TV that starts with the host of the show ringing a doorbell. My dog always thinks there is someone at our front door when this happens, but our doorbell has never worked. Clearly his former owners had a working doorbell. Here's a video of the skit. The audio and video quality are not very good, but this was the funniest version I could find on YouTube.
Beware: the volume is quite high.
http://www.youtube.com/embed/P3qUhG0CFvE
Damn you! I busted out laughing at work when he slipped at the end and nearly fell in!! LOOOL!!
What about this one? http://www.youtube.com/watch?v=kW-uFXVNe4k