If it gets to that stage where you need to sell your business you have to make sure you do it in the correct way to ensure you get the most money possible. There are plenty of places where you can advertise your company in order to get as much exposure as you can, the internet is becoming a popular place as more and more people are beginning to use it on a daily basis.
First off you have to decide how much you would be willing to accept for the company, make sure you have the relevant details such as revenue/profit, traffic (internet business) and any other information you think strengthens your sales pitch. This is vital as everyone will want to see proof of what you are claiming before they offer any money for it. It's advised that you get a professional help when it comes to valuing your business as they know what to look for and can make a fair judgement of how much it could sell for, you would hate to accept an offer lower then what it's worth without knowing.
Once you have the price in place you need to put together a sales description giving all the necessary good points and tell people why they should buy it. If you own an online business make sure you include screenshots of traffic stats, earnings and any good ranking keywords in the major search engines.
If you are advertising this online it would be better to go for a place that you have to pay a small fee to advertise your company, this means it will eliminate any time wasters from the very beginning making it easier to find a real buyer who is generally interested. There are many sites that will allow you to auction off your company, this can be good as people get into bidding wars and do what ever it takes to win!
Also make sure that you advertise it offline to get more exposure as not everyone has access to the internet and you could miss out on a buyer by not including it in the local papers, magazines or other places where they advertise businesses for sale.