The HAF 912 doesn't have a window by default. Unless you mod it to have a window, it doesn't make a lot of sense to put up flashy LEDs because you won't see it. LEDs are only cool for a little while. Afterwards, no one would care about it. And it'll all be a waste of money.
Edit: CRN beat me to it. Anyway, what's your budget for a case?
Under $100 if possible, but if theres a case that you feel is absolutely perfect then I'll go under $150.
Edit: Yeah I guess you are right. LED's are cool for a while then they will get boring and nobody will care. Still, I'm not asking for some Christmas lights on my case, I just don't want a completely dark case with nothing on it. I want just a little something to make my case standout.
What are some alternative to LED fans? CRN mentioned LED strips but how do those work and how to I know if my case can accommodate those?