Mine’s Bond and Goldfinger arguing about centrifugal force.
My second choice would be his Godwin’s Law panel.
And hasn’t everyone goofed up once in awhile and done a Fourier transform of their cat?
When’s Munroe gonna put out a book of his best strips? They’d sell like hotcakes.
My favourite is Useless, it’s just so damn sweet. 
Conspiracy Theories is my favorite. But I am also fond of Gyroscopes.
I love the “even the identity matrix doesn’t work normally” mouse-over.
I think my current favourite is Exploits of a Mom - SQL humour, gotta love it.
For a time, I really liked this one best of all: Battle Room , but I’ve gotten over the pin by now.
The all-time great is, of course, Words that End in -GRY
Mr. Dibble already mentioned my favorite, “Exploits of a Mom.”
The funny thing is how much that one has spread. Just try googling “Little Bobby Tables.”
A few of my favorites that have not already been mentioned…
Cat proximity is awesome, and so, so true.
90’s Flowchart is cute.
Grownups is sweet, and it would be fun to try that, or the blanket fort some time. And “Angular Momentum” is definitely an “awww”.
Hard to pick, because I have so many favorites, but “Grownups” is the one that first sprang to mind for me.
according to the site’s blag, Mr. Munroe did indeed pull it off.
This one is my favourite.
I… I’m speechless.
…
!
My favourite, too. I had it on my desktop for a long while. I’m just a big mushy mushball.
I love Commitment, on a pure comic timing level. Perfect.