We present spin-polarized scanning tunneling microscopy Measurements demonstrating spin-polarizations of tip to 80 % for Co islands on a Pt(111) surface and a tunnel magneto resistance of 850 similar to\% between the islands and an anti-ferromagnetic Cr-coated W-tip. These values remain constant up to +/-0.7 V bias. We report oil the magnetic moments and anisotropy energies of two-dimensional Co islands oil Pt(111) comprising only a few atoms. Our results show the correlation between orbital moments and magneto-crystalline anisotropies and reveal that both properties strongly depend oil the lateral atomic coordination. The anisotropy or single adatoms is found to be 200 times the Co hcp bulk value. We also present well ordered superlattices of Co islands self-assembled oil Au(788). The particles have uniaxial out-of-plane magnetization and no dipolar interactions. They present a model system for ultra-high density storage media since they have the most Uniform anisotropy energies and the highest density of non-interacting particles so far realized.