Historically, the handguns that typically appreciated in value where considered expensive or high end when new, and for them to see a real gain in value the model typically has to be discontinued or undergo some sort of drastic change. Think Colt Python. That said, a quality gun will typically hold its value if you keep it in good shape and don't do any irreversible modifications. However, they rarely see a real return on their investment when you adjust the original purchase price for inflation.
Colt's typically hold their value, with some rare limited edition models that increase in value if they become popular enough. The closest that I can recommend as a real investment piece will be their upcoming O1913 Reproduction model. The previous WWI repro's have appreciated since their limited runs have ended since they became very popular and the O1913 model is promising to be the most authentic reproduction yet.
"Si vis pacem, para bellum" - If you want peace, prepare for war.