If you use wordpress, you might consider using adsense plugins. This makes life easier by preventing you to insert the code for each and every post your make. There are several plugins that will automate the process.
Here are some of the most popular Google adsense wordpress plugins
Adsense Injection: A simple plugin that inserts your adsense code at a random position of the post. You will notice that most of us are beginning to become ad blind meaning that we don't care about advertisement anymore. Rotation of the ads at various positions is a plus point.
Adsense Deluxe: This plugin will allow you to insert adsense or yahoo publisher network ads into your posts. A great feature of this plugin is that you can see a preview page before publishing.
Adsense Inline: A simple but effective way of inserting adsense in blog posts. You will need to customize the adsense plugin in the editor. All you have to do is go to the editor after the plugin activation and go to adsense.php and look for "Begin Google Adsense code" and "End Google Adsense code" and replace the adsense code and hit the update button.
AdSense Manager: It is a plugin that allows you to add adpinion, adRoll, adBrite, commission junction, HTML Code, ShoppingAds and WidgetBucks code.
Google AdSense Widget: This is an adsense plugin for sidebars. You have to buy this plugin for 1 dollar. This is a plugin that requires no coding or template modification.
Adsense Beautifier: The name probably chosen so that your adsense codes looks beautiful and will earn you money. This is done by placing images next to your ads; however this may not be in accordance with Google terms and conditions.
Google Ad Wrap: This works by wrapping your adsense codes around posts and comments for better targeting.
WordPress MU AdSense Plugin: This adsense wordpress plugin allows you to insert both Google and Yahoo ads in your posts.
Adsense Deluxe: One of the most popular adsense plugin. This plugin allows you to insert adsense and yahoo ad codes automatically.
MightyAdsense: Again will allow you to insert codes without modifying the templates. However, it requires the use of the_excerpt_reloaded plugin if you are using excerpts for archiving. But if using full length posts, then it is not needed and the plugin can be used on its own.