We will discuss the state-of-the-art of self-organized atomic beam growth at single crystal surfaces enabling one to create well ordered superlattices of metal islands with sizes going all the way down to the single atom limit. We will focus on mutual interactions between adsorbed atoms mediated by Friedel oscillations in the 2D electron gas of a surface state, and on static templates with a periodic modulation of the binding energy for the adsorbed species. The templates to be discussed are strain relief patterns in thin films of metals, semiconductors, oxides, and nitrides. We then show model systems suited to explore the ultimate density limit of magnetic information storage. These are Co islands self-assembled on Au(788). The temperature dependence of the zero-field susceptibility @chi@ shows that the homogeneity in the anisotropy K and in the moment M would permit single particle bits, and that mutual interactions between the monodomain particles are absent up to densities of at least 26 Tera particles/in@super 2@. We further show results on the anisotropy of bimetallic islands as a function of their composition.