You can easily create your own simple text advertisements to place inside your posts, pages and other shortcode supported areas, you can create and manage the advertisement from one admin screen and it shows up everywhere you have used its shortcode. Text Advertisements is a very handy WordPress plugin which allows you create and edit text advertisements (very much similar to Google Text Ads) and display them via shortcode.
How To Create Text Advertisements?
Install and activate Text Advertisements plugin. After activation visit your admin area Dashboard -> Text Advertisements -> Add New Advertisement page.
Give your advertisement a title, add link, small description and publish it.
You can create multiple advertisements and they all can be managed from Dashboard -> Text Advertisements -> Text Advertisements (Main Page).
For displaying ads simply use
[Text-Advertisements] shortcode for displaying them. Editing the advertisements from Dashboard -> Text Advertisements page automatically updates them everywhere on your website.
Another plugin called Easy Text Links is also a good option for those who want to go professional in creating and selling text link in WordPress. This plugin is designed to help you make extra revenue from your website by selling text links to others. It automates the insertion and expiration of text ad links.