I have harmonized thirteen common scales, all staring on C. The goal was to follow the rules of classical harmonic theory: I succeeded, but I often had to use chords that are not common in classical music (e.g. bVII is very prevalent). There are other ways to harmonize these scales—some even follow the same rules that I did—but I chose to harmonize them the way that I did.
Feel free to download the harmonized scales: