We report a simple depletion potential that captures measured potentials and phase behavior for micrometer-sized colloids in the presence of unadsorbing charged micelles, charged nanoparticles, nonionic macromolecules, and nonionic hydrogel particles. Total internal reflection microscopy (TIRM) is used to measure net potentials between colloids and surfaces, and video microscopy (VM) is used to measure quasi-2D phase behavior in the same material systems. A modified Asakura-Oosawa (AO) depletion potential is developed to accurately quantify particle-wall potentials and interfacial crystallization via particle-particle potentials in Monte Carlo (MC) simulations. The modified AO potential includes effective depletant sizes, accurate osmotic equations of state, and partition coefficients. Partition coefficients are used as the sole adjustable fitting parameter, although an approach to their theoretical prediction from depletant density profiles is also presented. Our results demonstrate a model that accurately captures depletion interactions and phase behavior in a variety of material systems.