So far I have suggested:
Cities (sci-fi theme): Quantum, Singularity, Resonance, Horizon, Cosmos, Axiom, Etheric, Phlogiston.
Ships (major rivers): Ganges, Rio Grande, Thames, Orinoco, Nile, Rhine, Danube, Po, Mississippi, Amazon, Tweed.
Extra (scientists/explorers): Kepler, Copernicus, Halley, Newton, Cabot, Polo, Magellan, Cortez. CavScout also suggested Galileo and Columbus.