Oh well, I spent the whole day playing with photoshop so I didn't have time to prepare anything so chances are you have seen this ^_^
This is Hatsune Miku, world's most famous "virtual diva". Wth virtual diva? yeah, that's how people usually refer to her. She is basically a voice bank from a singing synthesizing program from Yamaha, Vocaloid 2. Pretty much you can use her to sing for you if you suck at it (and know japanese because is the language she is avaiable at)
She gained a lot of popularity thru japan and around the world after many developers used the voicebank to perform songs. What I find interesting about it is, that all the developers have been eventually creating her a "personality" thru all the songs they have been making. Da fk, how can they do that? I don't really think it was intentional, but the lyrics usually have a lot of meaning and often tell a story helped with anime-like images based on the original concept art of the voice bank. So at the end, new creatos took that as established and was base for the next songs and so on. Same happened with the new voicebanks they have been developing. Everyone has a different personality wich has been growing since they came out.
Below is a link of one of Mku's concerts. Wait how does a virtual character has a concert? Since they have become really really popular in Niconico Douga (Some kind of japanese youtube) the creators performed a concert with the most famous songs using a live band, but playbacking the vocals. And since they are japanese, they did a full hologram of Miku to sing for the gathering of japanese freaks. Just check it out!