There really isn't a 'free' way to advertise your cab company online. Nothing online is free when it comes to advertising your company, and the closest thing you can get to advertising is to sign up for a free website and advertise your company on your free website.
You can do that here www.caagal.com
The most reliable source for companies to advertise on one's website is by using Google Adsense. It's completely 100% free to use, but the website must have quality content.
You can advertise your business for sale for free at GlobalBX. Their website is http://www.GlobalBX.com Then you should also make a public announcement about your business for sale at ViewMemo.com
Advertise your rental properties for free at rentalbrokerage.com
you can but you have to send it to youtube/google and pay them to advertise your website
ADVERTISE!
Vistaprint or Zazzle are some of the website that does free business cards. The setback is that they will advertise on your card by printing their websites on it.
If you want to advertise a hotel online in India. greedenholidays.com is one of the hotel advertising website in india. there you can add your hotel images, tariffs by yourself, it's free to register.
A good place for you to advertise your semi online is at www.sellyoursemi.com. They are a specialized classified venue. And they also offer free listings.
Visit their website by clicking on the related link below. Here you can advertise anything for free! Cars for sale, Properties, Stuf for Sale, Dating & Personals, Animals, Boats for Sale, Advertisie your business and website... This is limited to only South African users
You can advertise a website any where you wish. Eg. Google, Facebook, Yahoo and many more. :)