Any negatively charged particle will do. You can even use an anti-proton. Lifetimes may be rather short, however.
Exotic atoms cast light on fundamental questions - CERN Courier

The Paul Scherrer Institut in Villigen has investigated pionic hydrogen (π^--p) and deuterium (π^--d), and DAFNE in Frascati has investigated their kaonic counterparts. Other no-less-important species include kaonic and antiprotonic helium, which have been studied at the Japanese High Energy Accelerator Research Organization (KEK) and CERN, and yet another exotic variety is formed by the non-baryonic π⁺- π^-(pionium) and πK atoms. Finally, the antihydrogen atom, pbar-e⁺, which CERN has copiously produced, is in a class of its own owing to its importance for testing the CPT theorem to extremely high precision.