You didn’t really think that was too obscure, did you?
I like this recent one; I feel like this sometimes; I laughed out loud at this one; and these two are probably my favorites.
For the last one, (NP-complete appetizers,) I actually enumerated all possible combinations and demonstrated that there was no exact match. Even NP-complete isn’t bad when you’re talking about a field of 6 inputs. 
7*2.15 = 15.05
A read a thread here a few months ago that had a xkcd link, I’ve been a faithful reader ever since. Now I’m going to lose an hour of my life going through to read the ALT text.
Damn, what other comics have hidden messages?
This one speaks to me.
In the author’s blog, he mentioned that there are two solutions, so you’re missing something. Are you only allowing each appetizer to be included once?
I guess that I did make that assumption. :smack: Or specifically, I was using a tool that I’d developed for an instance of the knapsack problem where that assumption applies.
I mean, sheesh, who orders multiple quantities of the same appetizer at dinner? 
Dinosaur Comics is one. (two hidden messages- one in the ALT text and one in the e-mail subject that comes up when you hover over and/or click on the “e-mail the author” link) Whether there are any others, I don’t know.
Curses! I am over 300 comics into that one and though I have been checking the alt tags I didn’t know that there was a another hidden joke. Now I am going to have to start over.
I’m not sure about anyone else but I have read more than enough journal articles on cryptography to have laughed pretty hard at that one.
Oh, and this one remains one of my favorites.
A Softer World does too.
The NBC show Heroes has an online comic. Clicking a page in the comic reveals a hidden photo. It isn’t hard to figure out the url naming patterns, so you can skip to all the photos without reading the associated comic.
I was very chuffed to learn that a friend of my SO’s went to school with the creator of xkcd, so I’m just two handshakes away from him. This is heart-warming, in a strange and mysterious way. I’ve been addicted to this comic since I was pointed to it a long time ago.
Okay, so I’m exploring the archive now. Damn you. I didn’t have time for this.
Best giggle so far (aside from the ones already cherry-picked above):
That’s one of my favorites.
I also like Irregular Webcomic’s parodies:
http://www.irregularwebcomic.net/1458.html
http://www.irregularwebcomic.net/1640.html
And answers my question about why I couldn’t read all the hidden text too…thanks!
(Firefox, btw…!)