We have fabricated and studied two-dimensional (2D) and three-dimensional (3D) metallo-dielectric photonic crystals (MDPC) in the visible/near ir spectral range using a variety of optical techniques. The 2D MDPC showed anomalous transmission due to surface plasmon polaritons in resonance with the photoluminescence band of a π-conjugated polymer based on a poly-phenylene-vinylene derivative. Consequently we fabricated an organic light emitting diode (OLED) using the 2D MDPC as a cathode with improved performance over an OLED with unperforated cathode. The 3D MDPCs are based on metal infiltrated opal photonic crystals. We studied the reflectivity spectrum of various metal infiltrated MDPCs and found that the reflectivity is low in the visible spectral range but dramatically increases towards the infrared revealing the elusive metallic gap. Our findings are in good agreement with recent theoretical and numerical calculations based on a commercial program.