Simulation of multiple small satellite accretion by James Bullock and Kathryn Johnson (2005 ApJ 635, 931)
see [movie - 9.4Mb]
Similar simulation by Paul Harding.
If a significant fraction of galaxy halo's are constructed in this way, one might expect to find evidence of substructures -- not just in physical space, but in velocity/physical phase space. Several projects are currently looking for such substructures in the Milky Way halo -- with some success.