This paper presents a self-organized grouping (SOG) method that achieves efficient Grid resource discovery by forming and maintaining autonomous resource groups. Each group dynamically aggregates a set of resources that are similar to each other in some pre-specified resource characteristic. The SOG method takes advantage of the strengths of both centralized and decentralized approaches that were previously developed for Grid/P2P resource discovery. The design of the SOG method minimizes the overhead incurred in forming and maintaining groups and maximizes resource discovery performance. The way SOG method handles resource discovery queries is metaphorically similar to searching for a word in an English dictionary by identifying its alphabetical groups at the first place. It is shown from a series of computational experiments that SOG method achieves more stable (i.e., independent of the factors such as resource densities, and Grid sizes) and efficient lookup performance than other existing approaches.