If you're headed for Topeka, Kansas, I can't say enough about avoiding Forbes Field, the commercial airport for Topeka.
You don't have to worry about a crowded airport or lines at the ticket counter. US Airways Express is the only commercial air carrier that services Forbes Field and there are only four departures and four arrivals daily (Saturday it's only one of each) to/from Kansas City, Missouri.
If you're not a fan of commuter airplanes, this will give you more reason to stay away from Forbes Field. US Airways Express flies the Beechcraft 1900 on the route between Topeka and Kansas City. It's a 19-seat plane that is a tight fit getting into.
The flight is just a short 15 to 20 minutes from Kansas City.
From my experience with Yellow Cab (785-357-4444), I can say without hesitation that you want to avoid them. I called the night before and asked for a cab to pick me up at 6:45AM for a 7:45AM flight out of Forbes Field. After three calls to them, they finally picked me up at the hotel at 7:20AM. I got to the airport at 7:39AM and luckily just made it under the wire to get on my flight. It also took them 40 minutes from the time I called to get a cab out to Forbes Field to pick me up and take me to my hotel.
The only other choices to call is Capitol City Taxi (785-267-3777) and Jayhawk-Checker Cab (785-234-8294). Both Yellow Cab and Capitol City Taxi can be called from a kiosk in the center of the terminal.
You can get a rental car at Forbes, but it's off-site. Although Hertz does have a counter at the airport when I was there, Hertz sent a car out to pick up anyone renting from them.
My suggestion is that if you need to go to Topeka, avoid Forbes Field and rental a car from Kansas City. With the trouble of getting a cab and long layovers in Kansas City when you fly from Topeka, you'll end up saving time and trouble for yourself.