One possiblity for your commute is an internal hub gear, such as a Nexus or Alfine. You get the simplicity of just one chainring and cog, with the gears when you need them. They are heavier than derailleur systems, and you need to stop pedalling for a second or two while you shift, but on the plus side you can shift while stopped at an intersection (useful in traffic). They are also a little more weather-proof as there is less exposed to the outside.