In case you're clueless about such virtual nonsense (and that's perfectly reasonable, mind you), I suggest a quick glance at the Wikipedia entry for lolcat. Here's a brief excerpt with the relevant info:
"A lolcat is an image combining a photograph, most frequently of a cat, with a humorous and idiosyncratic caption in (often) broken English—a dialect which is known as “lolspeak,” ”kitteh,” or “kitty pidgin” and which parodies the poor grammar typically attributed to Internet slang. The name "lolcat" is a compound word of the acronymic abbreviation "LOL" and the word "cat." A synonym for "lolcat" is cat macro, since the images are a type of image macro. Lolcats are designed for photo sharing imageboards and other internet forums."
Apparently, it all started on on image-board, 4chan.org, where users started posting "cat macros" sometimes involving immoral and disturbing acts. Very nerd-core, if you will. But lolcat first hit the public eye with this G-rated guy, circa 2007:

Then there was this one, which is a bit funnier and certainly more uncomfortable:

If you google search, you'll find 1000's, possibly millions, of these images. They used to pop up in the most annoying places, like message boards and comment lists, but nowadays seem to cluster on web-sites dedicated to the phenomenon: like the appropriately named icanhascheezburger.com and lolcats.com. However, picking through lolcats on these sites really demeans the experience - I find lolcat much more powerful and affecting when I encounter one randomly, in a place I otherwise wouldn't expect. Like when I was doing a google search the other day for "Force Field" and got this image:


Here's one that our friend LS found a little while ago and has been making the virtual rounds:

Some are self-referential and angry, which is cool in a post-modern, cynical kind of way:

Here's one that I would call "uber-nerdy": it combines lolcat, esoteric video game knowledge, and The Settlers of Catan boardgame. Holy fuck, I'm embarrassed.

Then there's this one, which was inevitable...



Finally, you should probably check out the Lolcat Bible Translation Project, where community users are attempting to translate every book, chapter and verse of the bible into lol-speak. Here's how it begins - Genesis 1:
"1 Oh hai. In teh beginnin Ceiling Cat maded teh skiez An da Urfs, but he did not eated dem.
2 Da Urfs no had shapez An haded dark face, An Ceiling Cat rode invisible bike over teh waterz.
3 At start, no has lyte. An Ceiling Cat sayz, i can haz lite? An lite wuz.
4 An Ceiling Cat sawed teh lite, to seez stuffs, An splitted teh lite from dark but taht wuz ok cuz kittehs can see in teh dark An not tripz over nethin.
5 An Ceiling Cat sayed light Day An dark no Day. It were FURST!!!1
6 An Ceiling Cat sayed, im in ur waterz makin a ceiling. But he no yet make a ur. An he maded a hole in teh Ceiling.
7 An Ceiling Cat doed teh skiez with waterz down An waterz up. It happen.
8 An Ceiling Cat sayed, i can has teh firmmint wich iz funny bibel naim 4 ceiling, so wuz teh twoth day."
