Scientists from NTT DoCoMo in Japan dreamed up this pair of headphones with cameras attached that can detect what you're gazing at within 20 degrees. The two cameras record the scene in front of you, while a cursor superimposed over that image indicates where you're looking. It works using EOG (Electro-oculography) sensors that can pick up small changes in electrical impulses when you move your eyes from one place to another.
Let's hope the researchers are working on a more aesthetically-pleasing implementation of this technology. It's not exactly something that will make you über attractive to the ladies, guys. Even so, this is quite a technological feat, and one that might be used in research, or perhaps even have military implications. However, all this technology may not even be necessary in some circumstances—for example, most large-breasted women can immediately tell exactly where you're looking without any such paraphernalia.
Full-time wearable headphone gaze detector presented by DoCoMo [InC innovative communication, via SciFi Tech]