A new article regarding the mirror test of self-recognition is making some pretty large waves.
The mirror test is fairly simple; apply a mark to some agent's forehead, so that the mark isn't visible unaided, then provide the agent with a mirror. If the agent rubs - or seems generally curious - about the new mark on its own head after looking at it in the mirror, then that's evidence that the agent recognised the reflection as being itself - self-recognition. Adult humans pass the test, small children don't. A few non-human animals pass, as well - great apes, dolphins, elephants.
What's interesting about this new study is that monkeys normally fail the test; what's different in this study? Instead of placing a mark on the monkeys, the monkeys had received implants for a prior experiment; in previous research into whether monkeys possessed mirror self-recognition (MSR), only a mark was used - one that only provided a visual stimulus, not a tactile one. We might assume (reasonably) that the implant provided an additional tactile stimulus, so the monkeys were receiving two forms of novel stimulation from this new addition to their forehead. This, presumably, provided the extra salience necessary to make the monkey pay attention to its reflection - and perhaps make the connection that this reflection was virtually identical to its self.
More discussion (and videos of the monkeys) here and here; I found Frans de Waal's comment that self awareness may occur on a gradual scale both interesting and very reasonable. This new study might not demonstrate that monkeys have self-awareness in the same way that humans do, but it may well demonstrate that they have the capacity for a relatively high degree of self awareness.
Rajala, A.Z., Reininger, K.R., Lancaster, K.M., & Populin, L.C. (2010), Rhesus Monkeys (Macaca mulatta) Do Recognize Themselves in the Mirror: Implications for the Evolution of Self-Recognition. PLoS ONE, 5(9): e12865. doi:10.1371/journal.pone.0012865