Unless you feel like buying a new set of tires every week, shining them up is going to be your next best option. A clean and shiny set of tires is one of the easiest and aesthetically pleasing elements of a well detailed car.
There are many products to choose from, most around the $10-$20 dollar range, and they usually go a long way. Simply spray on, and apply with a sponge. Keep it off the tire treads – just the side-walls. Also, unless you want marks all over your driveway, put down newspapers or something when you are spraying it on to keep any over-spray off the ground.
Check out this youtube link for a brief visual: https://www.youtube.com/watch?v=yBbsC1DALPo