Internet memes or phenomenons are everywhere these days and its hard to catch one early. There's nothing worse than sending something to a friend only to get back "that's so last week."

All your base, Little Superstar, Mosh Girl, Fat Asian Kid, Dramatic Prairie Dog, This is Spartaa all bring a smile to my face when I think of them. Wikipedia has a larger list of Memes but I feel its incomplete as Tron Guy certainly demands to be in there.

Memes vs Viral:
The way to think of a meme vs viral is like this. Viral is something advertising agencies create to try and sell a product and if popular will stay around for a few months.
A meme is something that changes the way people talk and will end up being mentioned on Family Guy or The Simpsons.

Another fancy word for Viral
If the word VIRAL feels overused and has lost its meaning then try using MEME. It hasn't hit the mainstream yet and if you explain it as I have it's like a Viral on steroids then when someone else pitches to do a Viral your ideas will sem better.
Note: You say it mehm not ME ME.

Untapped Memes:
Here's a couple new ones which I saw last week which have yet to catch on as much as the previous examples

Chocolate Rain

Algorithm Dance

If the Algorithm dance seems slightly odd what's even more odd are these Inmates from the Phillipines dancing to it

Or the same inmates reenacting Thriller.

Advertising Funded Memes:
It's interesting to note that very few of these memes actually helped any product get sold. Almost none were created by advertising agencies. Aside from Ford's Hurra Torpedo but they just latched onto an obscure band that already existed.

OK Go's career was saved with their treadmill film clip, Blair Witch and Snakes on a Plane would be forgotten if it not for the web. SNL is probably more popular now thanks to Youtube than it has ever been. (Narnia Rap and Dick in a Box)

Aside from these, very few were actually created with the purpose of selling something and I think that's because these things grow organically. When something is forced it rarely sees success.

The only two examples I can think of quickly are Subservient Chicken and Million Dollar Homepage. Both created solely to make money for someone and both wildly popular and spawned many imitators.