It is said that the Hubble space telescope has observed a ghostly ring of dark matter in the cluster CL0024+17. Sounds interesting! An earlier paper on this cluster may be found here. There is a noteworthy remark on page 6: compared to the weak lensing mass ... and the virial mass ... the mass deduced here from the X-ray observations is lower by a factor of 4. Matti Pitkanen says, "Rings puts bells ringing!."
In other news, the Cassini mission has been observing organic molecules in the atmosphere of Titan.
Update: Here is the dark ring image from NASA: Observe that this is a LARGE scale image. The weak lensing circle is barely visible at the inner edge of the dark ring. That means a LOT of 'dark matter'.